Law needs stability. Citizens must know what to expect from the law and what the law expects from them in a consistent, uniform and transparent manner. Yet the law is not static, but a living entity influenced by historical, cultural, and linguistic factors (Tampubolon 2025). In step with societal and technological developments, legislative acts are constantly amended and changed, while legal concepts are reinterpreted, legal principles reshaped, and doctrines reconsidered. Seen in this light, legal interpretation plays a crucial role in ensuring that the law remains relevant and effective (cf. Tampubolon 2025). Movement is hence necessary to achieve the binding unity of the law. This tension between movement and stability, diversity and uniformity, is clearly manifested through the example of EU law.

EU law is an iconic legal system. First of all, it was developed as an artificial legal construct out of the Treaties (EU law), lacking a common legal culture. Second, it is applied and interpreted by both national courts of the Member States and EU courts, thus operating in a twofold legal environment. Third, its adoption, application and interpretation is marked by the principle of equal authenticity. This principle renders all (at the moment 24) language versions of EU legislation equally authentic, authoritative and valid in 27 Member States. All of this leads to a unique legal landscape colored by the need for uniformity, while upholding equal authenticity and maintaining linguistic diversity.

A practical implication of EU law being applied, enforced and interpreted in multiple contexts by EU courts and national courts and institutions of the Member States is that these processes unfold in multiple languages. The multilingual context creates profound opportunities for both linguistic and conceptual divergence, and in consequence, undermines uniformity and political stability of EU law. While (linguistic and legal) ambiguity is inherent to the law, having 24 language versions of a single piece of legislation creates greater room for linguistic incongruence due to imperfect legal translation and the lack of absolute correspondence between languages. Linguistic incongruence and divergence may result in conceptual divergence of EU law and affect its uniform application across the Union. For example, the fact that the term ‘member of the household’ contained in Article 3(2) of the English version of the Directive 2004/38/EC on the right of Union citizens and their family members to move and reside freely within the territory of the Member States had been rendered as ‘viva con’ in Spanish and ‘convive’ in Italian, that is ‘inwonen’ in Dutch, was brought to light in case C-22/21. The latter three versions could imply less stringent requirements such as mere cohabitation under the same roof in order to consider someone (a non-EU citizen) as a member of the household (of an EU citizen). However, the terms used in other language versions of that provision (e.g. German ‘häusliche Gemeinschaft’, English ‘household’, French ‘ménage’) denote domestic life and all the activities and affairs linked to family life within the same household, i.e. more than the mere sharing of accommodation or a mere temporary cohabitation for reasons of pure convenience (C-22/21, p. 21). Pursuant to its well-established case-law, the Court of Justice of the EU in this case reiterated that provisions of EU law must be interpreted in light of all language versions while considering the context and the purpose of the relevant legislation. In other words, the provision in question must be given an independent and uniform meaning throughout the EU, in line with the purpose of this Directive, namely maintaining the unity of family in a broader sense; facilitating free movement and not deterring Union citizens from moving if other family members were not able to accompany them (Recital 6 of the Directive).

To cope with linguistic divergences, the Court has adopted hybrid interpretative methods that include literal interpretation and linguistic comparison supplemented by a contextual and teleological analysis. Most importantly, in resolving linguistic or conceptual divergence the Court relies heavily on the conceptual autonomy of EU concepts as well as on the principle of consistent interpretation, i.e. interpretation in conformity with EU law (Stawecki 2022). Therefore, if there are doubts about the meanings of certain provisions of EU law due to ambiguity or differences in the wordings between the language versions, conceptual autonomy allows the provisions in question to receive autonomous European meanings (independent of national-law concepts and their meanings within national legal systems). The Court strikes a fine balance between the need for interpreting EU law in light of all language versions and thereby upholding the political unity of linguistic diversity and conceptual autonomy which allows for uniform interpretation and construction of EU norms in light of the underlying purpose of the legislative act in question irrespective of its wording in different languages. In so far, the Court’s methods and the developed implicit principles of linguistic comparison and coherence safeguard the effectiveness and unity of EU law Union-wide.

Uniformity to the Detriment of Trust

However, tilting the balance in favour of conceptual autonomy, and not individual language versions, affects the desired transparency of EU law and subsequently trust of EU citizens in EU law. Even though equal authenticity implies that EU citizens may rely on their own language versions, as all versions are equally authentic and valid, prioritizing conceptual autonomy seems to push the role of language to the margins. What is more, it impacts citizens’ trust in EU law. Citizens as users of legal information tend to trust sources of information as authoritative (Callister 2023). Hence, trust forms an essential part of authority. If EU citizens cannot rely on their language versions of EU legislation to learn about their duties, rights or to save time and resources, but instead must rely on meanings of these provisions as construed by the Court, this impacts the cognitive authority of EU law, as well as uniformity and transparency. Transparency, as we know, builds trust.

Despite the need for stability of the law in order to ensure legal certainty, there is a „natural instability or ambiguity that exists within legal texts, rules, and doctrines” (Tampubolon 2025). EU law is a prime example of this inherent instability due to multiple authenticities of legislative acts and the resulting linguistic variation and potential conceptual divergence. Furthermore, conceptual divergence may stem from the lack of a common frame of reference and national differences in the conceptualization of EU concepts: e.g. the right of withdrawal might be conceptualized differently in Germany due to the local notion of ‘schwebende Unwirksamkeit‘ that is not part of other legal systems – which is an example of my earlier work on terminological variation and conceptual divergence in EU Law. As illustrated, through the use of conceptual autonomy and by underscoring the importance of consistent interpretation, linguistic comparison and coherence, the Court has managed to deal with the unique challenges of its legal landscape. Still, despite the existential importance of uniformity for EU law which has to function in a double legal environment, the related aspects of trust and transparency warrant more attention especially from the perspective of the citizens. Citizens’ legitimate expectations demand that they can rely on EU legislation in their own language. The same is true for national courts and law practitioners who read, apply and interpret EU law in their language versions. Yet, as posited in the Court’s settled case-law, the wording used in one language version of EU law cannot serve as the sole basis for the interpretation of that provision.  If citizens and national courts have to ‘wait’ for the Court of Justice of the EU to legitimize EU laws and validate the meaning of certain provisions of EU law, their trust in the authority of EU law is shaken. Therefore, the need for uniformity feeds distrust into EU law.

Can Digital and AI-based Tools Enhance Trust?

The requirement of transparency as enshrined in EU law (e.g. Article 15 Treaty on the Functioning of the EU) is crucial for it allows citizens to be aware of their rights and fosters trust. But how transparent can legal information truly be if judicial decisions are required to legitimize EU legislative acts in different languages? Increasing transparency and trust is especially relevant due to conceptual divergence of EU law such as the lack of common concepts, lack of common legal culture, or education, and the multilingual legal environment. This complex legal landscape feeds inconsistency and divergence (both linguistic and conceptual) and undermines the strong need for coherence and convergence in EU law. In this regard, the growing use of digital and AI-based tools in law might have a positive effect on transparency of EU law by enabling easier access to multilingual legal information and in turn furthering public trust. While legal interpretation is undoubtedly difficult to translate into a computational technique, recent studies ventured to investigate citizens’ trust in AI in the context of judicial decision-making. Some of the methods developed by the Court of Justice of the EU could also be partly computationalized (e.g., data-powered linguistic comparison as cognitive interpretation, e.g. Corpus linguistics in multilingual adjudication); whereas precedent-driven interpreting techniques could support the principle of consistent interpretation which is central to ensuring uniform application of EU law. At present however, it is difficult to assess if AI-powered tools could increase the authority of EU law or foster citizens’ trust. In any event, enhancing transparency about the Court’s decision-making taking place behind closed doors and the untransparent role of language in its adjudication is essential to building public trust.

Martina Bajčić is Associate Professor at the Law Faculty of the University of Rijeka; member of the Institute of European and Comparative Law; International Law and Language Association (ILLA), and the Austrian Association for Legal Linguistics (AALL). Her main research interests include legal terminology, EU multilingualism and legal interpretation as well as the intersections of law, language and technology.