Canon 365

Can. 365 §1. It is also the special function of a pontifical legate who at the same time acts as a legate to states according to the norms of international law:
1º to promote and foster relations between the Apostolic See and the authorities of the state;
2º to deal with questions which pertain to relations between Church and state and in a special way to deal with the drafting and implementation of concordats and other agreements of this type.

Can. 365 §2. In conducting the affairs mentioned in §1, a pontifical legate, as circumstances suggest, is not to neglect to seek the opinion and counsel of the bishops of the ecclesiastical jurisdiction and is to inform them of the course of affairs.