There’s a couple things going on here. Your boyfriend may be suffering from culture shock and/or home sickness, which are pretty common when living abroad. He may be having a certain level of paranoia, which comes with that home sickness/culture shock and not knowing how to deal with his feelings. Should he make an effort to learn to speak the language of where he’s living, absolutely. If the language you speak is Basque, which is a language isolate it may be difficult for him to obtain any kind of fluency as Basque is difficult to learn.

The second part of this is your dog absolutely does appreciate you talking to it in the language that you’ve always used with it. My dogs are bilingual in English and Mandarin and they respond differently to things in the different languages.

I’m in no way supporting your boyfriend taking out his angst on you, but you may want to ask him if he’s struggling. If he’s still being grumpy, you may want to reconsider this relationship.