Hello, @nils,
If you do not want to use the loco translate plugin and want to translate your site then, you have to use the poeditor software: https://poedit.net/
You can simply edit the po file with that software and then change the word/translation as per your requirements, after that you have to compile that po file to mo file using the same software because the machine will read the machine-oriented (mo) file.
Then after that, you have to put/upload the po and mo files under the directories listed below:
domain/wp-content/languages/themes/xstore-de_DE.po
domain/wp-content/languages/themes/xstore-de_DE.mo
It will work for you.
Regards 8Themes Team.