Hmmm, it's tricky
I have tried to learn a bit of Dutch and all of DP's family are always delighted when I give it a try - in fact, I sometimes get applause!! :o
But when I am there, they all try and speak English, even though I am the only non-Dutch speaker.
Sometimes, if we are all sitting around and the conversation is getting intense or complicated, someone will say "Do you mind if I just say this in Dutch? I don't know how to say it in English" and they speak Dutch for a while
If they are saying "Hey do you want a coffee?" they will say it in Dutch - but I can generally get the gist or, if I look puzzled, they will say "Oh sorry - i said...." in English
In general, I never feel like I am being excluded or laughed at because I don't speak their language. They try,in a friendly, open way, to include me when they can. In return, I try and say a few things in Dutch too which they really appreciate.
In short, I think it's about intent - do they intend to exclude you, or make you feel excluded, or are they just not thinking about how you feel. Speaking another language is not rude per se. But if they are doing it to purposely exclude you, it is