Formal:
* Diplomatic relations: This is a broad term encompassing all interactions between countries.
* Intergovernmental dialogue: Emphasizes the official nature of the communication.
* Bilateral discussions: Highlights the two-party nature of the talks.
* Summit meeting: Indicates a high-level meeting between heads of state or government.
* Treaty talks: Specifically refers to discussions aimed at reaching an agreement.
Informal:
* Talks: A general term for any form of communication.
* Discussions: Implies a more open and less formal exchange of ideas.
* Conferences: A larger gathering with a specific topic or agenda.
* Meetings: A more general term for any gathering of people.
The best word to use will depend on the specific context and the level of formality you want to convey.