Whenever a court is faced with potentially applicable foreign law they will turn to the Rules of Evidence and, in particular, the provisions for judicial notice. Judicial notice is the vehicle to determine the substance of applicable law coming from a different jurisdiction - whether that be a foreign country or a different state.
When the law comes from a foreign country, taking judicial notice will, first and foremost, require a foreign language translation of the legal text into English. In addition to this foreign language translation, the courts will turn to informal evidence, including affidavits and
treatises, to prove what the foreign law is. This too will likely require the use of both foreign language translations and, in some cases, foreign language court interpreters to interpret the testimony of experts.