Wrong default language

Hi,
After installing “WPGlobus” the website of a friend appears in english. So: https://www.domain.de is english and https://www.domain.de/de is the german site. I want it the other way around: https://www.domain.de should be the german site and https://www.domain.de/en should be the english site. What am I missing? Additon: The Plugin setting: Use browser language … doesn`t work either.
Thanks for any help.

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