Is AUTHOR wrong in the post ? POST : My SO is an immigrant, and English is not his first language (his first language is relatively obscure so I won't list it here). I do not speak his first language - I have been learning a bit so can understand some, but the pronunciation and grammar are very difficult for me (due to the different language roots, and my general lack of linguistic talent), so I really cannot speak it at all in a way that would be understood. Additionally, in the part of his country he's from people speak extremely quickly, so my ability to understand or respond appropriately in the course of normal conversation (as opposed to slow and clear learning exercises) is pretty much nil. Sometimes I'm able to guess what the conversation is about based on context and the odd word I can pick out, but that's about it. 

When we started dating, he still lived at home with his parents. When I'd visit, friends of the family would often be present, and we would often have conversations that would basically begin in English but quickly devolve into their native language. At this point I understood literally none of it, but I'd feel paralysed - people would still be looking at me as if I was part of the conversation, and every so often everyone would laugh or make an exclamation, but I'd have no clue what was going on! Sometimes I'd start to fiddle with my phone, and someone (never my SO) would shoot me a look or make an offhanded comment like I was being rude. I talked to my SO about it and he was like you're definitely not being rude, we're being rude by not including you, and he would constantly bring the conversation back to English but they'd basically ignore it. He'd go "come on guys, let's speak English!" and everyone would agree but then revert back within the space of a sentence or two. On some occasions it would end up with him literally carrying on his end of the conversation in English while everyone else would answer in the other language, which is actually pretty comedic if you think about it. I felt like a burden, after all it wasn't my house and I was the only one unable to speak this language while everyone else there was at least bilingual. Basically I ended up generally just sucking it up and being as polite and involved as possible.

So that was a long time ago, now. We moved in together after a couple of years and his family moved away, so it really hasn't been an issue. Until now.

Recently my SO's mother has moved back nearby. She has started coming over once or twice a week, which really is not a problem for me - she's his mother, after all, I like her well enough, and she rarely outstays her welcome. Her English is good, and she's fine with staying in English when chatting with both me and him. However, over the last few weeks, she's started inviting over some family friends in the area every now and again, with our permission of course. I like most of these people and have chatted with all, they are all professionals who speak fluent English. But for whatever reason, when they're all together, the conversation always ends up changing to the other language. My SO has been trying the same conversation tactics to switch language, with the same results. His mother is no help in that respect whatsoever. It's just like before, except now I feel way more put out about it, because I'm not the guest or the outsider any more - it's my house. I feel like I can't get a word in edgeways or cut in because the way they speak, it's like they're all shouting over each other - no gaps at all. 

I talked to my SO about it. I said that I don't particularly want to stop them from coming over, and to be honest it doesn't even bother me too much if they want to hang out and chat without me, I just hate being in the room and feeling ignored. He suggested that if they start to do it again, to get up and just leave, and that maybe that will also drive home to them how rude they are being. So I tried it, and the results were... Not great. My SO had tried again to ask them to switch to English but as always, it didn't stick. So I grabbed a glass of water and just left without saying anything to go watch TV in the bedroom. Soon after I heard some shouting and then the front door slamming a bunch... Apparently, my leaving the room caused several family friends to immediately start bitching about me being rude, which cause my SO to blow up and tell everybody to get out, which has now caused significant strife between my SO, his mother, and their friends. I haven't seen her since. 

I feel like such an asshole. I know they were being rude but at the end of the day I'm the one who doesn't speak their language, and I can see how to talk a completely different language for the benefit of one person is inconvenient to say the least. I feel like I've fucked up my relationship with my MIL! My SO says that they are the assholes, and I was entitled to be as rude as I liked because they were being disrespectful from the start. I'm not sure if that scans. What do you guys think? 

TL;DR AITA for being rude and walking out mid-sentence because the group was not speaking English, causing a rift between my SO and friends and pissing off my MIL? Or ATTA for not speaking English in the first place? 