The traditional US restatement view on choice of law is that the governing law for a contract must be the law of a jurisdiction with which one of the parties has some relation or contact. Vienna Convention on Contracts for the International Sale of Goods. Conceptually, you should think of this as an international version of the UCC Article 2. The convention will apply to any commercial sale of goods transaction between parties with places of business in countries that are signatories of the convention - unless the parties specifically opt out. If there is a sales transaction involving parties that are located in countries that are convention signatories, and there is no contract, or a limited contract with key provisions missing, the convention will be the first place that a court is supposed to look to determine the rights of the parties with respect to the sale.
Most commentators seem to consider the convention inadequate in the area of force majeure.
For this and other reasons, it is the norm for international sales contracts to contain detailed force majeure terms and not to rely on either the convention or any local law provision. These are the standard trade delivery terms used in international contracts. The latest iteration is Incoterms 2000. Don't use state law trade terms for international contracts - use Incoterms. Currency of Payment.