Which they are.

Agree, it’s rude af.

Sure, if people suddenly switched languages and then laughed in my face, I would feel bad.

But if it’s like the other comments in this post, and it’s a couple having a quick word about a private matter, I wouldn’t mind. It’s not like I should be a part of that conversation

This varies depending on the cultural norms of the country.

Japanese: I have been in high level meetings with a Japanese company. As soon as I walked into the room they all switched to English. Some of their English was weak but they still made the effort. When I commented on how much I appreciated it, surprised Pikachu faces all around. They responded course they would swap, to do otherwise is rude.

In France I have had business meetings with with 8 people around a table all of who all spoke english. 4 of them were native French speakers, 1 polish, 2 Arabic, and me the sole native English speaker. The native French speakers spoke French the entire time. They would swap to English to interrupt the English language conversation then swap back to French amongst themselve. If two or more native French speakers are together, they speak French and don’t give a fuck if they include you or not. They then act all surprised that you didn’t follow their in French conversation.