What does it mean if a girl says “this conversation is relaxing for me”?

[RyanEC]

It’s a girl I was talking to from Iran.
We were talking on a language learning app.

We were talking about shared interests and how I think our two countries should talk more.

[_Maya_]

It means exactly that. It is a relaxing conversation and she enjoys it because it isn't about politics or anything else similar to that where people can get heated. It is just about your shared interests and life in general. There is nothing negative about what she said so don't over think this. I am guessing since you are both on a language learning app she maybe thought those were the best words to use instead of I am enjoying the conversation or what have you.