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.

[Timedifference]

So, a few of us are going away to celebrate a big birthday.
SIL is coming without her husband cos he doesn't like flying and the birthday boy has picked an overseas destination.

We go on Thursday. I found out today she's coming.
She tends to monopolise my DH when she's with him - ive got a horrible feeling she'll be whispering in his ear most of the time. I hope im wrong.

AIBU to not look forward to this break anymore?
I don't want her to be lonely but she fusses over him like hes a child and I get shoved to one side.

Is it your DHs sister?

Yes, his sister.

What does your DH say? It’s great they get on, rubbish If you’re excluded

DH hasn't said anything
She might want to have a relaxing time in a beach resort and sleep, read & eat, so I might be getting ahead of myself.
I hope I am

I already feel excluded when they speak another language in front of me.

Oh I wouldn't be having that. I would just say "In English please" every time (or better still secretly learn their language yourself 🤭).

Have you spoken to your husband about how her actions make you feel?

Tell your DH that the minute he starts conversing with his sister in their own language, you feel excluded, and it makes you unhappy, so please can he refrain from doing it. If he then goes ahead and does it anyway, you'd have every right to make a fuss.

As for his sister, just don't let her push in, if you want his attention, make sure YOU are the one who gets it, you wouldn't let another woman push in, would you, so don't let her.

You need to tell him to stop leaving you out.

I can't help feeling you've picked the wrong thread title though.

It should read more like "My DH always leaves me out when he gets together with his sister".

I will tell them in English please.
I need to tread a fine line between being rude to her & standing up to myself.
My relationship with DH is rocky at the moment and I dont want her shoving her nose in.
She thinks im an ungrateful cow and thinks the sun shines out of his bum.

Itll be good for his family to see that hes a workaholic and leaves loads to me.
They dont believe he works on holiday for 6 hours a day.
Hes not self employed.

Hes booked this break cos I said im not booking another holiday where you work every day.
I checked the plane seats and hes booked the seats going but not coming back! So we've got middle seats on a long flight. Not good for me.

Yes, your title is really misleading and your OP doesn't clarify. I assumed your brother's wife was trying to move in on your husband.

Also, it's standing up FOR yourself, not TO. You'd be standing up to her.

Use Google translate and beat them at their game

It’s weird that you have an issue with your husband getting on with his own sister.

It sounds like you’re not happy in your marriage and seeing your husband happy in someone else’s company makes your bitter and jealous.

@Timedifference
I think you need to list all your problems with your DH for yourself ( it seems there are a lot of them) and then ask us about each of them separately.
I don’t think SIL’s husband not going to this celebration holiday is your main problem.

You got bigger problems tbh.

SIL being close to her brother is really a non-issue. Don't project your marital problems on her.

You can't really tell them they are not allowed to speak to each other in their own language unless there is just the three of you there. If his family aren't from an English speaking country then it's up to you to learn their language if you want to integrate if you need to understand what everybody says all the time.

Having said that, it is completely blantanty clear that your issue is that yours and you DHs relationship is rocky and you can't face him having fun with somebody else, including his own family. Don't take this out at your SIL, it will only damage yours and your DHs relationship further.

Just say to them both pease don’t be rude, please speak in English otherwise I have to assume you are talking about me and that’s not nice

and repeat

I think you're right - I have got bigger problems.
Its one thing after another.

I'm afraid I think it's pretty rude that you haven't bothered to learn your husband's language

I understand a bit but I cant keep up after a few minutes.
She also speaks in a low voice to him, and I cant hear half of it.

He can have fun with other people, that's not an issue.
Its the buzz buzz in his ear.

Please stop blaming this woman because your husband treats you so badly.

She tends to monopolise my DH when she's with him - ive got a horrible feeling she'll be whispering in his ear most of the time.

What kind of a weirdo whispers into her married brothers ear and wants to monopolise his time. And what kind of a weirdo married man would be 'happy' with this.