I really appreciate you do all the work to put this plugin in other languages.
But the problem for me is that I will have to change every lang file after I had to delete them for an update to change terms in there like "scrap" instead of "money". I really don't wanna do this for every language every time. :)
So, is there a way to only use the english version for every player?

You can enforce a language on your server using Oxide by using the 'lang en' command in your server's console or RCON. A plugin having other language files isn't going to hurt anything otherwise. You also do not need to delete the files every update.

Putting this in console manually would only last til server restart or wipe? Right?
Is there a command I can put in the start.bat or server.cfg maybe that plugins only use the english lang file and do that forever?
I cannot change every language file there is to fit to every player. I don't speak russian, french or spanish. :)

The command is a server preference, it is set when you set it and stored in Oxide's oxide.lang.data file.

Ok. Thank you.
One more thing. Will it only affect the plugins and their language or will the complete game be in english then if they play on my server?
And how can I set this back to normal if I don't like that?

It would only affect messages from the plugins, not their client. I'm not 100% sure this actually works though, since the default is English anyway; so may be something we'll have to look into changing a bit.