When the law crosses borders: the challenge of proving foreign law

In an increasingly globalized legal context, litigations with international elements have become a frequent reality in Spanish courts. The mobility of people and goods, along with the transnational component of legal relationships, has intensified the need to apply foreign norms in national proceedings, raising significant procedural challenges.

One of the most persistent challenges faced by our courts has been determining how to proceed when the controversy requires the application of a foreign law that the parties have neither invoked nor proved, as required by Article 281.2 of the Civil Procedure Act.

Traditionally, the Supreme Court had leaned —with some jurisprudential fluctuations— towards a practical solution: applying Spanish substantive law subsidiarily to resolve the controversy and ensure effective judicial protection. However, this position has not been without criticism, as in practice it meant circumventing the mandatory conflict rule due to the parties' passivity in presenting evidence. From a procedural perspective, foreign law, even if it is 'law', must be proved.

This doctrine has led to paradoxical situations, such as parties deliberately avoiding arguing or demonstrating the content of foreign law, thus seeking the direct application of Spanish law because it was more favourable to them. It cannot be denied that proving the content and validity of a foreign norm is a complex and costly task, but the question is inevitable: can a party avoid the application of a mandatory norm simply by omitting to allege and prove it?

The Supreme Court, in its ruling on 30 October 2024, sought to put an end to this practice and establish a new course, as had already been advanced in the Supreme Court ruling of 3 April 2018. From now on, the subsidiary application of Spanish law will be reserved for truly exceptional cases: it will only be applied when it is genuinely impossible to prove the applicable foreign law due to extraordinary causes, such as wars, pandemics, or similar disasters. In summary, the Supreme Court has sought to reinforce the notion of "exceptionality" provided in Article 33.3 of Law 29/2015.

This change in jurisprudence marks a new, stricter paradigm: it is up to the claimant to allege the applicable foreign law and demonstrate its validity and content, unless there are factual situations that justify the impossibility of proving this law. These proofs may be supplemented by the court, but they can never be substituted. Therefore, if the claimant does not prove the foreign law, the only possible response will be to dismiss the claim. Meanwhile, the defendant is not obliged to prove the foreign law, unless they choose to file a counterclaim based on it.

In light of the new jurisprudential doctrine, which was also agreed upon in a plenary ruling, dissenting voices have quickly emerged questioning in particular the Supreme Court's criterion regarding who should bear the burden of proving foreign law. For some legal professionals, it would be logical for this burden to fall on the party seeking to benefit from its application, whether the claimant or the defendant. This position is based on a more flexible and functional view of the process.

However, another sector —aligned with the interpretation of the High Court— argues that when the application of foreign law is evident and has been deliberately ignored by the claimant in a 'forum shopping' maneuver, the defendant cannot be required to compensate for this omission. In other words, if the claimant has strategically chosen not to invoke foreign law to benefit from a more favourable national legislation, the burden of proving what, by legal imperative, was their responsibility should fall on the claimant and not be transferred to the defendant.

This doctrinal debate, far from being resolved, has generated controversy for over a year. And what is more worrying: provincial courts have not adopted a uniform criterion following the ruling of the High Court, leaving legal professionals in a state of uncertainty, where each case could be left to the discretion of the judging court. This situation calls for prudence and procedural strategy.

As an illustration of the existing contradictory jurisprudence, it is worth mentioning, in accordance with the doctrine of the Supreme Court, the ruling of the Provincial Court of Malaga of 13 February 2025 (no. 106/2025, rec. 897/2022), and, in a divergent sense, the ruling of the Provincial Court of Barcelona of 4 April 2025 (no. 512/2025, rec. 103/2024).

In any case, the recent doctrine of the Supreme Court represents a step towards greater coherence in the application of private international law, reinforcing the requirement for proof of foreign law as an indispensable condition not only for its application but also to allow the exercise of the action which, in the absence of proof, could be dismissed outright.

This change, although not without discrepancies, aims to prevent procedural abuses and ensure that conflict norms do not remain empty of content due to the inaction of the parties. However, the disparity of criteria among provincial courts shows that there is still a long way to go to achieve a uniform interpretation.

In this scenario, it is essential that legal professionals remain attentive to the evolution of jurisprudence and act diligently and cautiously when proving foreign law, thereby contributing to legal certainty in cross-border litigations.

Access the full article written by Ruth Sánchez and Amaya Urgoiti, from the Litigation and Arbitration department of ECIJA Madrid, published in El Confidencial here.