SIL coming on family celebration holiday without her husband. (MNHQ update at OP's request) Now everyone is chatting in their own language and excluding me.

Your choice to stay behind. They've tried to include you.

Absolutely, how arrogant (and embarrassing) to demand the language people speak is yours!

If the rest of the party speak x language then it’s op that should learn new language or live with not understanding

I also don't see the issue with the walk.

You should remind them English please for conversations when you are present.

You sound awkward and like you have an issue with everything.

If I was visiting family and they told me to be ready for 12 as they’d planned a nice walk for us I wouldn’t see it as an issue.

My DHs sode of the family speak fouent English 2nd Language yet when they are together choose theie 1st language ane exclude me. I have also said to him many times how bloody rude it is. As me and my parents are fluent in Arabic and we never use it infeont of him or exclude him even though my Dad prefera Arabic he chooses English to not make my DH feel left out. But my inlaws don't give a crap.

She is entitled to go on the holiday, why isn't your focus on your DH, surely he has a voice to speak up for you.
He is aware that it makes you feel uncomfortable, yet he participates happily.

Maybe they’re catching up on family business. Just go have fun with the children and not worry so much about.

Why did you marry someone and learn learn to speak their language, you were always going to feel left out!

OP have you ever read Pride and Prejudice? Lady Catherine De Bourgh would say “I MUST have my share in the conversation!”

Or you could say ‘What are you two whispering about?’

This. And also how is it the sister monopolising his time? Why is it being framed as if she’s the one controlling this?

He’s a grown man and if she really is ignoring all of you and he does the same - well he is fully complicit and is the one you should be focused on, OP.

Neither of my brothers have kids but I have a close male friend with two young kids and a wife. When I spend time with them I couldn’t “monopolise” his time even if I wanted to.

I don’t think he would stand for his family being ignored and also his wife goes out of her way to welcome me so we have our own chats. She also encourages the kids to interact with “Aunty”.

Basically they all make feel so welcome. But even if that wasn’t the case I just can’t imagine constantly pulling my mate away for whispered chats the whole time , ignoring his whole family and him being ok and going along with all that.

Agree with others, you can't tell them to speak in English, I don't think you understand how rude that would be. My DH is French, when we see his family I understand hes going to speak to them in French most of the time and its fine, its just a small bit of time in the years we have together.

Why is your SIL getting the heat for your rubbish H and rocky marriage? I get that it’s easier pointing the finger, then dealing with the problem but won’t change anything.

@CopperWhite That's exactly it. I am not from an English speaking country either. I obviously understand and speak it but it would feel very strange and unnatural for me to only speak to my family in English because there is somebody around who doesn't speak our language. I would obviously speak English if that person is involved in the conversation, but I wouldn't be speaking to my sister in English just because the person who don't understand is in the vicinity. Doesn't mean we are gossiping about that person or that we are trying to be rude, it just means that we are speaking to each other in the language we have been using since we were toddlers.

There is going to be a buzz buzz in his ear and they will speak their own language because that’s what they grew up speaking to one another in.

Honestly, I really think you’ve just got to be the bigger person here. Accept they gossip and they will enjoy it and let them get on with it. Be friendly and go into this weekend thinking come Hell or Highwater you’ll have a good time. Sit next to someone else at dinner who you like.

You can’t reasonably stop a brother and sister communicating in the language they grew up using. Their relationship is not about you.

Obviously I don’t know how fluent they both are in English but it can be exhausting for some people to be forced to constantly talk in their second or third language. This is not how people should be made to feel when they are spending time with their family. You shouldn’t be deliberately excluded, but they shouldn’t have to revolve all their chat around you being able to understand either.

Make some effort to learn their language and you might feel less excluded.

Then don’t say ‘please speak English’
Say ‘please stop whispering, it’s rude’
or ’Please speak up, I can’t hear’

Your husband doesn't sound very nice, OP.

Regarding the seats on the plane - can you change your seat?

Yeah my friend married a Vietnamese woman and he learned the language. Another friend did the same with learning Korean after her Korean fiancé moved to the UK for her.

Some Languages can be hard so fair play if you can’t learn it to a decent level
but don’t agree you should be trying to stop them conversing in their native language.

My partner is Spanish and I’m trying to learn Spanish - both for myself and for him too. I’ve always enjoyed languages though and I appreciate it’s not the same for everyone.