Volume 32 Issue 2, June 2026: p. 227-242
P-ISSN: 1693-0061, E-I SSN: 2614-2961
https://fhukum.unpatti.ac.id/jurnal/sasi

: 10.47268/sasi.v32i2.3696

Normative Tensions between International Law and Customary Legal Systems: Comparative Insights from Indonesia and Spain

Wa Ode Zamrud^1*, Antonio Gutiérrez Pozo²

^1, Faculty of Law, Universitas Dayanu Ikhsanuddin, Bau-Bau, Indonesia.
^2, Facultad de Filosofía, Universidad de Sevilla, Sevilla, Spain.

: waodezamrud@unidayan.ac.id
Corresponding Author^*

INTRODUCTION

The interaction between international law and the national legal system is increasingly intense and complex in the era of legal globalization. This dynamic encourages the formation of a network of legal norms that are cross-border, where universal principles become a reference for countries. However, on the other hand, every country has its legal heritage, cultural values, and social traditions that shape its national legal identity.¹ When global norms meet local legal practices, conceptual and practical friction often arises that are difficult to avoid. This phenomenon is referred to as the normative tension between international law and the local or customary legal system.

Normative tension can be understood as a situation when two or more of the prevailing legal systems simultaneously make different claims of legitimacy to the same social behavior.² International law in this context, prioritizes the principles of uniformity and universality, while customary law contains a particular dimension that is rooted in community values.³ The interaction between these two legal systems poses a dilemma for the state in determining normative priorities whether to comply with international obligations or to maintain local wisdom. These tensions are not only a matter of formal law, but also of political and social legitimacy in the formation of national legal policies.

Indonesia is one of the countries with a high level of legal pluralism, where national law, religious law, and customary law interact dynamically.⁴ Customary law has a strong historical and sociological position as a reflection of the cultural identity of local communities.⁵ International legal norms in practice arise challenges when, especially in the fields of human rights, the environment, and the rights of indigenous peoples, they are faced with a customary law system that is oriented towards communality.⁶ As is the case with the implementation of the Free, Prior and Informed Consent (FPIC) principle in the context of natural resource management, it often raises debates between the interests of national development and the protection of customary rights.⁷ This situation shows that normative tensions in Indonesia are not just theoretical, but have a real impact on policy and social justice.

In addition, the unwritten and flexible character of customary law in Indonesia is often at odds with the nature of international law which tends to be rigid and codified.⁸ This poses difficulties in legal harmonization because the two systems have different legitimacy mechanisms. International law is based on formal treaties and conventions, while customary law is rooted in social consensus and continuity of tradition.⁹ The Indonesian government faces a dilemma between fulfilling international commitments and maintaining the sustainability of customary law as part of its national identity. This inconsistency often leads to the marginalization of customary law in the national formal justice system that prioritizes written and positivistic evidence. As a result, the customary law system is forced to adopt a Western formality structure in order to be recognized at the international level, which in the process risks eroding the original values of customary law itself.¹⁰

Spain constitutionally recognizes legal pluralism through the integration of customary legal traditions (Derecho Foral) in regions such as Catalonia, the Basque Country, and Galicia into the national legal system.¹¹ The existence of this customary law creates a unique dynamic in which normative tensions not only occur between international and national law, but also involve central law with autonomous regional law. The application of international norms in practice regarding minority rights in Spain often clashes with domestic political sensitivities related to regional identity.¹² This poses the challenge of harmonizing global standards with local legal sovereignty that has deep historical roots. Spain provides an important perspective on how modern countries in Europe manage the dialectic between the universality of international rights and the particularity of the local legal tradition.

Normative tensions in Spain are further complicated by the influence of EU law that demands the integration of supranational legal standards into domestic jurisdictions.¹³ The Derecho Foral often has to negotiate not only with the Spanish Constitution, but also with European regulations that prioritize market unification and civil law.¹⁴ Clashes arise when specific customary local law traditions regarding property ownership or inheritance law are considered to impede the principles of non-discrimination and freedom of movement that are enshrined in international legal instruments.¹⁵ These dynamics suggest that constitutional recognition alone is not enough to defuse tensions if it is not accompanied by a clear normative dispute resolution mechanism.

The Spanish judicial system through the Constitutional Court acts as a mediator in reconciling global demands with local values.¹⁶ Courts must weigh the extent to which international standards can be adapted without violating historically guaranteed principles of regional autonomy. These tensions are often resolved through a proportionality approach, in which the universal importance of international law is tested against the protection of legitimate regional legal identity.¹⁷ This Spanish experience shows that reconciliation between global and local law requires a very high degree of judicial interpretation flexibility in order to maintain political stability and national legal legitimacy.

Indonesia and Spain show different forms of legal pluralism but have similarities in dealing with the pressure of legal globalization. Indonesia represents a model of pluralism born out of the postcolonial context and ethnic pluralism, while Spain reflects legal pluralism within the framework of democratic and institutionalized states in Europe. Comparisons between the two allow for a cross-contextual analysis of how international norms are negotiated in legal systems with different degrees of integration. By conducting a comparative study between Indonesia and Spain, the research can reveal the extent to which customary law or customary law is able to adapt to the principles of international law without losing its social legitimacy. This approach can also show a universal pattern in the management of normative tensions between legal systems.

The urgency of this research lies in the need to identify a more inclusive and equitable model of legal interaction between the international legal system and customary law. The success of a country in negotiating the relationship between these two systems is an indicator of adaptability to global changes. This research is expected to contribute to the development of the theory of legal pluralism and offer practical recommendations for countries with similar legal structures.

Research by R. R. Dewi Anggraeni in AHKAM: Journal of Sharia Science highlights the complexity of legal pluralism in Indonesia, particularly the tension between Islamic law and customary law within the framework of the modern legal state. The study found that the legal system in Indonesia often experiences normative fragmentation due to the overlap between national law, religious law, and customary law. Although this research makes an important contribution to understanding the dynamics of pluralistic law in Indonesia, its focus is still limited to the domestic context and has not yet linked these tensions to international legal norms. In addition, Anggraeni's research has not developed cross-border comparative analysis that can enrich understanding of how other countries navigate the relationship between global norms and local laws. Therefore, there is a research gap in explaining how legal pluralism in Indonesia interacts with the principles of international law in a more comparative and conceptual way.¹⁸

Meanwhile, Josep Maria de Dios Marcer and Josep Cañabate Pérez in Legal Cultures describe in depth the structure and characteristics of Spanish law, including the relationship between national law and local customary law. The study shows that the Spanish legal system accommodates plurality through constitutional mechanisms, but still affirms the supremacy of national law over customary law. Their findings highlight that normative tensions in the Spanish context are more institutional and political than cultural as in Indonesia. Although this research provides a solid foundation for understanding legal pluralism in Spain, its approach is descriptive and has not critically elaborated on the relationship between the local legal system and international legal norms. In addition, there has been no attempt to place the Spanish context in cross-cultural comparisons that can show variations in legal adaptation to the globalization of international norms.¹⁹

This research offers a scientific novelty by combining comparative and normative-analytical approaches to explain the tension between international law and customary law systems through Indonesian and Spanish case studies. Unlike previous studies that tended to be domestic and descriptive, this study places both countries within the framework of cross-legal system analysis to identify universal and contextual patterns in the management of legal pluralism. This approach introduces the concept of "cross-systems normative dialogue" which emphasizes the process of negotiation between global norms and local values as a conceptual solution to normative conflicts. Thus, this research not only fills the gap in the literature on the relationship between international law and customary law, but also offers a new paradigm in understanding legal pluralism as a dynamic interaction space between universal legitimacy and cultural particularity.

The purpose of this study is to analyze comparatively the form and character of normative tensions between international law and customary law systems in Indonesia and Spain, taking into account the social, political, and institutional factors behind them. This research also aims to identify the legal approaches used by both countries in negotiating the relationship between international norms and local values. In addition, this research seeks to formulate a model of legal harmonization that is adaptive to global legal pluralism, in order to bridge the tension between the universal principles of international law and the cultural particularities that live in the national legal system.

METHODS OF THE RESEARCH

This research uses a type of normative legal research, which focuses on the analysis of legal norms, principles, and doctrines related to the relationship between international law and customary law systems. The approaches used are a comparative approach and a conceptual approach, with the aim of understanding the differences and similarities in the management of normative tensions between Indonesia and Spain and formulating a theoretical framework that is more adaptive to global legal pluralism. The primary legal materials used include international treaties and conventions, the constitutions of the two countries, and laws and regulations governing the recognition and protection of customary law. Secondary legal materials consist of academic journals, books, research reports, and relevant scientific publications. Meanwhile, tertiary legal materials include legal dictionaries, legal encyclopedias, and online resources that support the interpretation of legal concepts terminologically. Data processing techniques are carried out through inventory, classification, and systematization of legal materials based on the research theme. The data analysis technique uses a qualitative-descriptive analysis method with deductive reasoning to draw normative conclusions that explain the pattern and model of harmonization between international law and customary law in the context of Indonesia and Spain.

RESULTS AND DISCUSSION

1. Normative Tensions Between International Law and the Customary Law System in Indonesia and Spain

Normative tensions between international law and customary law systems arise when universal principles of international law are adopted into local contexts that have different value systems. Norms in international law, such as self-determination, equality before the law, and individual human rights are considered universal values that must be accepted by all nations.²⁰ However, in indigenous peoples, legal legitimacy is not only based on individual rights, but on collective balance, spirituality, and harmony with nature.²¹ In Indonesia and Spain, the application of the principles of international law often creates friction when customary values cannot be accommodated within such a universal framework. This form of normative tension is more ideological and epistemological, a clash between universal legality and customary legitimacy.

The United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) in 2007 is an international instrument that influences the formulation of policies related to indigenous peoples in Indonesia. Article 3 of UNDRIP affirms that indigenous communities have the right to determine their own political status and socio-cultural development. However, in the context of Indonesian customary law, the concept of customary sovereignty does not stand politically, but as a spiritual and social expression in the community structure.²² The formal adoption of the principle of self-determination has created tensions as the value of communal spirituality is forced to be translated into the concept of modern political sovereignty,²³ this is a form of conceptual clash between international law and the customary law system through the different meanings of "self-determination."

The character of tension is also seen in the implementation of the principle of Free, Prior and Informed Consent (FPIC) as stipulated in Article 32 paragraph (2) of the UNDRIP, which states that “States shall consult and cooperate in good faith with the indigenous peoples ... in order to obtain their free and informed consent prior to the approval of any project affecting their lands or resources.” Collective decisions in the context of Indonesian customs, are taken through customary deliberation (consensus deliberation) which is a spiritual consensus, not a rational legal contract.²⁴ The application of the FPIC principle with the logic of international law emphasizing formal procedures and written consent documents reduces the social significance of customs. This shows a form of normative tension that is methodological, namely between international legal rationality and the deliberative spirituality of indigenous peoples.

Normative tensions in Indonesia are reinforced by the structure of indigenous peoples based on social hierarchy and the value of collective spirituality, which is fundamentally different from the principle of individual equality emphasized in the 1966 International Covenant on Civil and Political Rights (ICCPR). Although Article 27 of the ICCPR provides protection for the right of minorities to enjoy their culture, this instrument still places "individual" as the primary legal subject through the phrase "persons belonging to...". Tensions arise when this principle of individual equality of international law demands internal democratization in indigenous peoples. This in many cases is actually considered to erode the traditional hierarchical structure that is the pillar of their identity where the traditional structure places traditional leaders (tribal chiefs, traditional elders) as representative figures.²⁵ So that the manifestation of this tension is not only a matter of cultural protection, but a contradiction between the concept of individual autonomy carried by global norms and the hierarchical authority firmly held by the local customary law system.

Political factors are the main catalyst that exacerbates the tension between international norms and customary law in Indonesia. After the ratification of international instruments such as the ICCPR and ICESCR through Law Number 12 of 2005, Indonesia faced great pressure to align local legal practices with global human rights standards. Tensions arise when international standards, such as the principle of gender equality in inheritance or formal criminal adjudication procedures, are confronted with customary law that has a logic of social sanctions and tradition-based division of roles.²⁶ Normative tensions are political-interpretive in that international law is often positioned by state actors as instruments of social reform, while indigenous communities interpret it as a form of legal imperialism that threatens their identity and autonomy.

Normative tensions in Indonesia arise due to the absence of formal mechanisms that allow for direct interaction between the international legal system and customary institutions. This relationship is fully mediated by the state holding sole authority as the interpreter of global norms into the domestic context. The essence of customary law in this translation process is often reduced to just an administrative instrument that must be subject to the logic of the state bureaucracy. This tension is vertical in that indigenous peoples have to fight as individual applicants or community groups against state laws before the Constitutional Court.²⁷ Customary institutions in Indonesia do not yet have a strong institutional bargaining position. Therefore, the character of normative tension in Indonesia can be precisely defined as "asymmetrical translation", a condition of structural imbalance in which international legal values are forced into customary spaces through positivistic state filters.²⁸ This tension is not just a communication issue, but a form of institutional marginalization in which customary law is forced to adapt to the language of state law in order to be internationally recognized.

In Spain, the normative tension between international law and the local customary law system (Derecho Foral) arises in the dialectic between minority rights and state sovereignty.²⁹ Although Article 2 of the 1978 Spanish Constitution recognizes the right to autonomy for various nationalities and regions, it simultaneously affirms the principle of "the undivided unity of the Spanish nation". The character of this tension becomes very complex when international norms regarding self-determination come into contact with local legal traditions (fuero) that have deep historical legitimacy. On the one hand, international instruments encourage the recognition of the collective identity of autonomous communities as independent political entities, but on the other hand, Spain's national legal system imposes strict restrictions in order to maintain constitutional integrity.

This situation creates a character of tension that is defensive-legalistic. Spain tends to interpret international norms on minorities restrictively so as not to open up opportunities for separatist movements in regions such as Catalonia or the Basque Country.³⁰ In contrast to Indonesia's more sociological context, tensions in Spain are a discursive battle over the extent to which local legal traditions can be recognized as subjects of international law without undermining the structure of the unitary state. So customary law in Spain functions not only as a local legal system, but also as a political instrument in the negotiation of sovereignty between the central government, regional authorities, and global legal standards.

Sociologically, autonomous communities in Spain such as the Basque and Catalan peoples interpret their legal identity as a manifestation of the collective memory and historical legitimacy that preceded the formation of the state. However, the principle of cultural protection set out in Article 27 of the ICCPR is often interpreted by international instruments through the lens of liberal individualism, where cultural rights are seen as individual rights.³¹ On the other hand, for the people of the autonomous regions of Spain, customary law (Derecho Foral) is a collective-historical right that cannot be reduced to mere individual preference.³² When international norms atomize cultural rights into personal rights, local communities perceive it as an obscuration of the essence of their community's struggle to maintain the sovereignty of traditions. So that the normative tension that arises has an ontological-semantic character, namely the existence of a fundamental disconnection in the meaning of "cultural rights" between international law and local customary law. International law tends to provide protection in the form of individual non-discrimination, while the customary law system in Spain demands recognition of collective entities that have independent legal authority.

Political factors in Spain significantly deepen normative tensions through interpretive contestation of the principles of international law. The Catalan independence movement used Article 1 of the ICCPR on self-determination as an instrument of legitimacy to justify the independence referendum in 2017.³³ However, the Spanish Constitutional Court through Decision 114/2017 rejected the claim by affirming that the principle of self-determination in international law does not automatically apply to entities in democratic states that have sovereign and guarantee territorial integrity.³⁴ These dynamics show that normative tensions in Spain are strategic-political, where local communities selectively use global norms to strengthen their political bargaining positions, while the state interprets the same norms as protection against constitutional stability.

In the institutional dimension, Spain presents a more structured form of normative tension than Indonesia. Although Spain has ratified instruments such as the European Charter for Regional or Minority Languages (1992), the implementation of these rights at the level of autonomous regions has often experienced administrative obstacles triggered by the centralistic policies of the central government. In contrast to Indonesia, which experiences asymmetrical translation through bureaucracy, in Spain this tension is facilitated through formal legal mechanisms where the national judiciary becomes the main arena of the battle between global values and regional legal traditions (fuero).³⁵ This condition shows that legal pluralism in Spain has been institutionalized in such a way that any tension between international standards and local customary law always boils down to a highly formalistic constitutional adjudication.

The form and character of normative tensions between international law and customary law systems in Indonesia and Spain show contextual differences but similar patterns. In Indonesia, tensions have vertical-asymmetrical characteristics, where conflict stems from the process of "translating" universal values into a spiritual-communal customary structure through positivistic state bureaucratic filters. In contrast, in Spain the tension is horizontal-institutional, which arises in the arena of judicial negotiations between the universality of international norms and the politically institutionalized tradition of customary law (fuero). These differences confirm that social, political, and institutional factors in both countries make the adoption of the principles of international law a process that is never neutral. The principles of international law have always been the subject of negotiation, adaptation, and even resistance by local legal systems that uphold their own moral and historical legitimacy.

2. Inter-Normative Dialogue Between Internasional Law and Local Legal Systems: Lessons from Indonesia and Spain

The negotiation between international legal norms and local values is a major conceptual challenge in the context of global legal pluralism. International law operates on the principle of universality establishing standards that apply across countries and cultures, while local legal systems are built on social legitimacy, traditions, and particular values. These two frameworks are in the process of adoption, so they often interact with each other, negotiating the space of validity between the "living law" and the "binding law".³⁶ This dialectic creates a space for debate about moral and political legitimacy between universal principles of human rights and contextual local values. These tensions demand a model of legal approach that is not just subordinative, but dialogical and adaptive.

Indonesia takes an integrative-normative approach by placing the principles of international law within the framework of Pancasila values and customary law. Through the ratification of the International Covenant on Civil and Political Rights (ICCPR) and the International Covenant on Economic, Social and Cultural Rights (ICESCR) in Law Number 12 of 2005, Indonesia is committed to international human rights standards.³⁷ However, the implementation process does not take place in a mechanistic-positivistic manner, but through the mechanism of translating culture into the values of deliberation, mutual cooperation, and communal balance. The international legal framework is not positioned as a subordinate system, but rather as an additional normative layer that enriches the national legal system.

Indonesia's approach to negotiating international and customary norms is evident in the process of recontextualizing global values at the local level. The principle of self-determination in Article 3 of UNDRIP is translated not as the political sovereignty of indigenous peoples, but as socio-cultural autonomy to govern themselves within the boundaries of national unity. This process is a form of semantic adaptation, in which often abstract-individualistic concepts of international law are drawn into a communal-spiritual local paradigm without reducing the substance of their fundamental rights.³⁸ This model reflects contextual universalism, which is an attempt to absorb universal values while maintaining the sociological legitimacy of customary law.³⁹ So that Indonesia does not just carry out formal synchronization, but presents an inter-normative dialogue pattern that is able to respect the spiritual authority of customary law while fulfilling the standards of its international obligations in an adaptive and harmonious manner.

On the institutional side, the Constitutional Court and the National Human Rights Commission are the main mediators in the negotiation process between international norms and customary law. The Constitutional Court Decision No. 35/PUU-X/2012 which affirms that "customary forests are not state forests" shows how the principle of indigenous peoples' land rights in UNDRIP can be interpreted in the context of national law. State institutions serve as translators of global values into local legal frameworks, creating a state-facilitated harmonization model.⁴⁰ However, this process is often hampered by disparities between judicial authority and administrative capacity. Although normatively recognized, the operationalization of international principles often hits the administrative labyrinth at the regional level, where the recognition of indigenous peoples is still highly dependent on a positivistic bureaucracy. This results in the success of legal harmonization in Indonesia not only determined by the interpretation ability of judges, but also by the ability of national institutions to transform global obligations into public policies that are in harmony with socio-cultural realities at the local level.

The approach to legal negotiation in Indonesia also shows a social-participatory character based on community mechanisms. Global human rights values in various indigenous communities, such as gender equality and environmental rights, are not adopted as top-down state instructions, but through a translation process in customary deliberation spaces. The principle of Free, Prior and Informed Consent (FPIC) mandated in Article 32 of the UNDRIP is not understood simply as a formal administrative procedure, but is translated into a communal moral obligation to conduct collective deliberation. This process confirms that the internalization of international norms can be achieved without eroding customary authority, but rather strengthening it. This form of negotiation represents a model of organic adaptation, in which universal values are "fused" into the deliberative process typical of indigenous peoples. The Inter-normative Dialogue framework, this phenomenon shows that customary law is capable of being adaptive and dynamic, proving that the universality of human rights can find its most effective form when it is in harmony with the social structure and morality of the local people.

Spain presents a multilevel model of constitutionalism in negotiating international norms with its local laws. Since the ratification of the European Convention on Human Rights (ECHR) and the European Charter for Regional or Minority Languages (1992), Spain has sought to balance international obligations with regional autonomy. Spain's 1978 Constitution Article 2 affirms the principle of national unity, but also recognizes "the right of autonomy for nationalities and territories." On this basis, international law is integrated through a multi-level system in which central governments, autonomous regions and EU institutions interact with each other within a layered legal framework.

The application of multilevel constitutionalism in Spain effectively creates a space for inter-normative dialogue structured between international standards and local legal traditions. Catalonia interprets the principle of self-determination by translating it as the right to cultural identity and administrative autonomy in order to avoid direct conflict with the principle of unitarianism of the national constitution.⁴¹ On the other hand, the central government conducts counter-negotiations by amplifying the principle of territorial integrity sourced from the UN Charter to maintain the cohesion of the country. This pattern of interaction shows the use of a "jurisdictional accommodation" approach, in which the state provides a measurable space of legal autonomy for regional regions as an instrument of political stability while maintaining compliance with international norms.⁴² Thus the negotiations in Spain took place entirely in the institutional-formal realm.

Spanish legal institutions, especially the Tribunal Constitucional play an important role in balancing international norms and local law. The Court in Decision 31/2015 affirmed that the principle of self-determination stipulated in the ICCPR cannot be used to separate oneself from the state, but can be the basis for cultural autonomy.⁴³ This interpretation reflects a legalistic-hierarchical pattern of negotiations, in which international norms are not adopted rawly, but are filtered through strict constitutional "filters". Spain puts forward a model of institutional harmonization that puts any potential normative tension into formal mechanisms of judicial testing. The framework of global legal pluralism is not allowed to develop wildly at the sociological level, but rather is managed as a formal legal discourse.

Spain also stands out in efforts to harmonize socio-cultural through local language and identity policies. The implementation of the European Charter for Regional or Minority Languages provides protection for regional languages such as Catalan, Basque, and Galician.⁴⁴ International principles on the preservation of local culture are translated into education policies and public administration at the regional level. This phenomenon shows that legal negotiations in Spain go beyond the boundaries of the constitutional text and enter the realm of recognition politics. Spain's Inter-normative Dialogue framework shows that international norms can be a "weapon" for regional regions to strengthen their bargaining position against the central government. The emerging tensions prove that the harmonization of global law with local values is not a static end product, but a continuous discursive process that is constantly negotiated within strict domestic political boundaries.

Indonesia and Spain present two contrasting but complementary models of legal negotiation in the discourse of global legal pluralism. Indonesia emphasizes the approach of substantive contextualism, which is the translation of universal meanings into indigenous social and spiritual structures. Spain, on the other hand, adopts an approach of institutional pluralism, in which differences in norms are accommodated through constitutional legal mechanisms and regional autonomy. These two models show that legal harmonization is not synonymous with uniformity, but rather openness to dialogue between legal values.

Socio-political factors are important determinants in the effectiveness of the harmonization model. In Indonesia, the success of legal pluralism depends heavily on the political will of the state to provide formal recognition of indigenous peoples, while in Spain its stability rests on the balance of power between the central and regional governments. When the political context is conducive, international norms are easier to internalize because they are not perceived as a threat to national identity. On the contrary, in tense political situations, universal values are often rejected in the name of local sovereignty, this shows that negotiations between international and local norms are not only a matter of law, but also an expression of power relations and identity.

The adaptive legal harmonization model requires a dialogical-interactive approach that prioritizes communication between value systems. Indonesia exemplifies the importance of moral and spiritual dimensions in adapting international norms, while Spain demonstrates the effectiveness of constitutional mechanisms in managing legal plurality. A conceptual model that can be proposed is the Adaptive Legal Pluralism Framework, which operates through three dimensions: (a) normative reinterpretation of global values, (b) institutionalization of cross-level legal dialogue, and (c) internalization of universal values within local cultural frameworks. Through this framework, global legal pluralism is no longer positioned as a source of fragmentation or conflict, but rather as a dynamic forum for strategic collaboration between different legal systems to achieve substantive justice.

CONCLUSION

Normative tensions between international law and customary law systems arise when universal principles of international law are adopted into local contexts that have different value systems. In Indonesia, these tensions appear in the form of asymmetrical translation, where the state acts as the dominant filter that often reduces the social meaning of indigenous peoples to an administrative framework. In contrast, in Spain the tension is horizontal-institutional, where international norms interact with the customary laws of the region (fuero) through formal constitutional mechanisms. negotiations between international legal norms and local values in Indonesia and Spain show that global legal pluralism demands an adaptive, dialogical, and contextual approach. Indonesia displays a contextual universalism model that emphasizes the internalization of global values into the moral and spiritual framework of customary law, while Spain implements institutional pluralism through constitutional mechanisms and regional autonomy. Both approaches prove that legal harmonization is not achieved through uniformity, but through inter-normative dialogue that respects local differences and legitimacy. This study recommends the need to strengthen participatory and layered inter-normative dialogue between international legal institutions, states, and local communities. In Indonesia, the establishment of consultative mechanisms that directly involve indigenous institutions in the ratification and implementation process of international instruments will narrow the gap between global norms and local values. The government needs to review the functions of the National Human Rights Commission and the Constitutional Court so that they not only act as interpreters of international law, but also as social mediators who ensure that universal principles are applied without eroding the autonomy of customary law. In Spain, strengthening coordination between levels of government (central–regional–EU) needs to be directed at ensuring the implementation of multilevel constitutionalism that truly respects the diversity of local law without threatening national integrity. This research suggests the development of the Adaptive Legal Pluralism Framework as a new paradigm of harmonization of international law and customary law, a model that emphasizes the epistemic equivalence between universal norms and particular values in a just and contextual global legal systeml.

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