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Thanks for the help :)

if you change your browser settings language it should change the language.

Well, my browser is in English, as well as my OS. So that's not it. But I'm located in Germany so it must be that. Anyway, a possibility to change it manually is much needed.

it doesn't use your ip at all to detect language, it uses your browser. You definately have your browser settings in german somehow somewhere

I agree there should be an option to control it directly inside DTube however

I actually think I "solved" it by deleting the German dictionary for spell checking. Now it's in English. So, thank you very much.

Great, thank you. I had same problem