What term best describes legal matters that involve two states?

The term that best describes legal matters involving two states is "interstate." This term specifically refers to interactions and legal issues that cross state lines or involve more than one state within a country. For instance, in the United States, interstate commerce refers to trade and economic activities that occur across state borders, which can also encompass various legal matters such as transportation of goods, jurisdiction between state laws, and conflict of laws.

In contrast, the term "intrastate" pertains to matters confined within a single state, indicating that they do not cross state lines. "Transnational" typically relates to activities or legal issues that span across nations, making it unsuitable when discussing legal matters between states within the same country. Lastly, "international" refers to interactions or legal concerns that occur between different countries altogether, further distinguishing it from the concept of matters occurring between two states. Thus, "interstate" accurately captures the essence of legal matters involving two states.