Federal Rule of Civil Procedure 44.1
Rule 44.1. Determining Foreign Law
A party who intends to raise an issue about a foreign country’s law must give notice by a pleading or other writing. In determining foreign law, the court may consider any relevant material or source, including testimony, whether or not submitted by a party or admissible under the Federal Rules of Evidence. The court’s determination must be treated as a ruling on a question of law.