International Arbitration: French Court Of Cassation Clarifies Its Approach To Dual Nationals In ISDS Through Two Significant Decisions On Treaty Interpretation

Two key decisions from the French Court of Cassation (First Civil Chamber) issued on 6 May 2026 deal with the question of dual nationals in ISDS arbitration and the application to treaty interpretation of Article 31 of the Vienna Convention on the Law of Treaties 1969 (the Vienna Convention). While the decisions reached opposite practical results, they are indicative of the highly methodological and detailed approach of the French Court of Cassation in dealing with issues of international law, and will have practical significance for treaty interpretation going forward.

These cases were decided in the context of the jurisdictional hurdle faced by dual nationals to bring bilateral investment treaty (BIT) arbitration claims against a state of which they hold nationality, a question recently before several Courts internationally.

A brief case note follows. The decisions can be found here: Cass. civ. 1ère, 6 May 2026, n° 24-10.445; Cass. civ. 1ère, 6 May 2026, n° 24-21.876.

Dangelas v. Vietnam

The dispute arose after the Claimant, Vietnamese by birth and later naturalized as a United States (US) citizen, invested in the Kien Luong Thermal Complex Power Project in Vietnam. Following an alleged expropriation by the Vietnamese government, the Claimant commenced arbitration under the UNCITRAL rules, invoking protections under the US-Vietnam BIT. Vietnam challenged jurisdiction from the outset, on the basis that the Claimant, as a dual citizen, did not fall within the scope of the BIT. In an award dated 8 December 2021, the tribunal recognised jurisdiction, finding that the Claimant met the unambiguous definition of the term ‘national’ and that the BIT did not impose any additional criteria in relation to dual nationals.¹

On 7 March 2022, Vietnam applied to the Paris Court of Appeal to set aside the tribunal’s award on jurisdiction, arguing that:

• in accordance with Article 31 of the Vienna Convention, a “treaty must be interpreted in good faith, in accordance with the ordinary meaning of its terms, in their context and in light of its object and purpose”;
• the scope and meaning of the BIT must thus be interpreted in light of the parties’ common intention, which can transpire from any further agreement in that respect;
• on 4 April 2023, the US embassy in Hanoi issued a diplomatic note, whose authenticity was undisputed, stating that “dual nationals are treated as having the nationality of their dominant and effective nationality for the purposes of submitting a claim under international law”; and
• accordingly, the BIT did not preclude dual nationals from bringing claims pursuant to the BIT.

The Paris Court of Appeal rejected Vietnam’s challenge, disregarding the diplomatic note as “merely an opinion from the economic section of the United States Embassy”.²

On appeal, the French Court of Cassation annulled the Paris Court of Appeal decision, holding that:

• a treaty must be interpreted in light of “any subsequent agreement between the parties regarding the interpretation of the treaty or the application of its provisions”;
• the diplomatic note established an agreement between the US and Vietnam for the purposes of interpreting the BIT; and
• by ignoring the diplomatic note, the Paris Court of Appeal had breached Article 31 of the Vienna Convention.

García Armas and García Gruber v. Venezuela

The Claimants were two individuals: a man, born in Spain in 1944, who later acquired Venezuelan nationality in 1972 (and regained Spanish nationality in 2004 after a ban on dual nationality ended), and his daughter, born in Venezuela in 1980 who took Spanish nationality in 2003. After the Venezuelan authorities confiscated the Claimants’ investments in the Venezuelan food distribution sector, they commenced UNCITRAL arbitration under the Spain-Venezuela BIT. The tribunal established jurisdiction in an award issued on 15 December 2014 (following a challenge by Venezuela based on the Claimants’ dual nationality), and later awarded damages of $370 million in an award dated 26 April 2019.

On 29 January 2022, Venezuela brought a challenge to that award in the Paris Court of Appeal, arguing that the Claimants were not entitled to rely on the Spain-Venezuela BIT because:

• pursuant to public international law, Claimants could not rely on their Spanish nationality in their relationship with Venezuela because they were also Venezuelan nationals; and
• in any event, the Claimants only acquired their Spanish nationality after they made the investments that were the subject matter of the dispute such that the requirement of the investments being made by a national of the other contracting state was not met.

The Paris Court of Appeal, and subsequently the French Court of Cassation, rejected Venezuela’s arguments on jurisdiction, holding that:

• a BIT constitutes a lex specialis between the contracting states;
• the sole requirement of the BIT was that an investor be a national of one contracting state, and in accordance with the ordinary meaning of these terms, this did not exclude the possibility for an investor also holding the nationality of the other contracting state;
• where a BIT contains clearly worded provisions to delimit its scope, as also confirmed in the travaux préparatoires as well as the BIT’s overall structure, recourse may not be had to other rules of public international law, including diplomatic protection principles, to fill the silence of the BIT on dual nationals; and
• the BIT did not exclude dual nationals from entitlement thereunder.

This decision confirms the approach of the French Court de Cassation in Ibrahim Aboukhalil v Senegal,³ whereby the Court declined to make a distinction for dual nationals where the France-Senegal BIT itself did not.

The French Court of Cassation’s Approach to Treaty Interpretation

Read together, the two decisions confirm that:

• the treaty remains the starting point and the wording must be considered strictly;
• general international law (including diplomatic protection principles) cannot automatically be imported to change the scope of treaty protection, unless the contracting states clearly intended to do so; however
• States retain the power to refine the interpretation of the treaty through subsequent agreements, including post-treaty interpretative notes.

They also evidence the long-standing practice of French courts to exercise a de novo review over jurisdictional challenges in investment treaty arbitrations pursuant to Article 1520(1) of the French Code of Civil Procedure.

The decision reinforces the importance of considering subsequent agreements and diplomatic exchanges in treaty interpretation, as well as the primacy of the actual text when interpreting a treaty. The decision may influence future treaty interpretation disputes in French courts and beyond, broadening the scope for what may constitute an “agreement” for the purposes of Article 31(3)(a) of the Vienna Convention, though limiting the scope to import international law principles where not expressly addressed by the parties to the treaty.

Our international disputes team is on hand to assist with any queries following this decision.

Footnotes

1. Dangelas and others v. Socialist Republic of Viet Nam (PCA Case No. 2020-05) (Decision on Jurisdiction) (10 December 2021)

2. Cour d’appel [CA] Paris, 1e ch., 12 September 2023, 15e ch, No. 22/05075.

3. Cass. civ. 1ère, 17 May 2023, n° 21-25.377.

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