If my friend has a jewish minecraft server, am I allowed to swear?

You should check the house rules for that server. It will tell you what is and is not permitted.

The game will allow it, but the moderators may boot/ban you for it if it is against their rules.

I think the swearing on a Christian Minecraft server was a meme what i would do is if the server is a public one check the rules and if its private ask your friend