The Library has many collections of information on foreign and international law. Before getting started, it's often helpful to characterize what you're looking for: "Foreign Law" refers to the law of individual non-U.S. countries (e.g. the Chinese Penal Code), while "International Law" refers to the law between countries.
The latter can deal with treaties, agreements, or conventions between two countries (such as extradition treaties or trade agreements), or the same types of agreements between larger numbers of countries (such as the treaty that established the United Nations.) The collections described on this page deal with both kinds of law, and contain both primary and secondary sources.