Hi Jan,

To translate or rename theme strings, you can do this via Loco Translate plugin. If you don't have it, please install and activate the plugin in your WordPress site.

1. Then go to Loco Translate > Manage Translations
2. Click "New Language" for the current active theme (if you didn't created it yet, otherwise ignore this step). On the new language page, choose these options – Screenshot
3. After that you will be redirected to the editing screen for theme translations. Before you continue with your translations make sure the current language of your site is selected – Screenshot
4. Follow these instructions to learn how to translate strings – Screenshot
5. The changes will be applied immediately – Screenshot

Note: Translation files will be saved to wp-content/themes/{theme-name}/languages folder or global directory of theme translations: wp-content/languages/themes/ (based on your choice). 

If you have saved your translations inside theme folder, always save a backup of languages/ folder (inside the theme) when there is new theme update. After you update the theme (languages folder will be replaced with an empty folder), just move the backup files you previously saved to the same languages directory and your changes will still be applied.

Happy to hear that, have a great day