8 year old swearing

[Usernameabcdwxyz]

Not a proper step parent but after 2.5 years in a relationship I have started to spend time with my BF‘s children.
He decided it was time as his ex is pregnant with her new boyfriend and she has been telling the DC that my BF is now alone with no family and that the DC are no longer part of his family.
We are abroad, so rights of fathers very different here.
DD8 was in the back of the car playing a game on a mobile phone. I kept hearing her saying „fuck“. They DC don’t speak English, neither does my BF.
With English being my mother tongue I was a bit offended. I don’t like hearing that word coming out of small mouths. My DC is an adult now and while she was brought up with other languages she knew this word was not allowed.
I told BF that it wasn’t very nice that she was saying it. He said tell her that in your language it is a bad word.
So I explained in her language and gave asked her if she would ever use a certain word in her language and she said no, my mum would go mad if I said that.
Now it turns out that it is the mum and the boyfriend that say fuck and DD8 had said usernameabcdwxyz said that is a really bad word in English 😂 and now the ex is complaining that I shouldn’t be parenting her children.
What do others think? Should I have just kept quiet?

No, you did the right thing. Though I would argue that really your BF should have addressed it with his DD not told you to tell her, he’s her father and supposed to be putting boundaries in place and teaching her respect.
That said, I was in the same situation (and trust me, it spreads into other areas when they don’t set boundaries).
My SD kept swearing when she was around that age. My DH used never called her out on it, unless I prompted him. In the end I decided I didn’t need to listen to that in my own home and my own DC was not allowed to swear despite being older so it was a house rule and she had to follow it.
Each time she swore I said her name in a ‘shocked’ tone, then said “we don’t use language like that in this house”. It only happened probably twice after I first called her out on it, each time she looked quite sheepish and embarrassed when I called her out. I think the issue was before that she was being made to think it was allowed because no one said anything.

My response to DH ex if she had complained would have been “I’m sorry that I had to teach your child how to behave appropriately when she has a mother already”

At the end of the day, his children will be in your life and your home, and while there are some things you can’t get involved with, if it affects you then you absolutely can. Why should you put up with bad behaviour?
Also, it sounds like she’s quite happy for her boyfriend to be a parent (saying they are the family now and your DH isn’t)

Oh yes, the her new boyfriend of 9 months definitely behaves like a parent but she’s 5 months pregnant by him. 🤷🏼‍♀️
My BF felt he couldn’t explain it as well to her because it doesn’t have the same feeling for him when someone says fuck. If she said shit in their language he would say something definitely.
I will be helping her out with her English in a few years when she starts at school so I really don’t want her swearing.
I have only met the ex once, and that was only 2 weeks ago. So I’m being told what she is saying to my BF.
I think this might be fun…….

Just ignore her mother. Are you really going to take criticism from a woman who allows her 8yo to swear? Your involvement with her DD is none of her business as long as she isn't coming to harm. If your OH is happy for you to parent her then that's all that matters. It sounds like your intentions are good and you care about her.