Speaking another language when one person doesn't understand.

I've been reading a few people's stories about this topic to see if I'm simply overreacting cause I tend to do so but I want to hear your guy's opinion.

Today I was on a discord call with my friend, she's swedish and I'm German obviously we always talk in English because we both speak it comfortably and it's the only language we speak in common. We were playing and met some other people, one person was danish and the other people were swedish too. I'm gonna refer to them as Mike who is the swedish guy and Rick as the Danish guy. When Rick and Mike were both there Mike spoke perfect English, talking to me through voice chat and chat, he was obviously comfortable in the language, we then decided to all call on discord. Well Mike started talking swedish to my friend, while me and Rick couldn't understand but only once or twice. After Rick left it, it was pretty common for Mike to just start a conversation in swedish while I obviously don't understand. My friend told him that I didn't understand and he should translate or say it in English, for some reason he never understood. Every time he was reminded he just never said it in English or just continued talking in swedish, my friend also always replied in swedish instead of replying in English so I would understand a little bit which was honestly a little weird. After a while I kinda got sick of it and made jokes like "yes I totally understand" or "I suddenly can speak swedish". Another friend of Mike joined and again it was mostly swedish. I didn't want to leave because I didn't want to be rude, so I just took it. After a while we kinda established that we said "English" when someone talked in swedish. My friend talked a lot more swedish which I can definitely understand why she all of a sudden swore in swedish again which she never did or stopped to do after a while of us talking. While I can understand it's normal to switch to your native tongue when another native speaker is there but I found it incredibly rude that he had to be reminded multiple times and didn't even stop right after being reminded nor cared to translate. I also found it slightly rude of my friend to reply in swedish or try to explain anything(which she did sometimes but not all times). It also couldn't be anything private because we just met and it was things like "I'm gonna go talk to my mom" etc. So I wanna know if this is reasonable for me to be mad about or not? (Sorry about the long text)