You need to use Loco translate plugin – https://xstore.helpscoutdocs.com/article/30-base-theme-translation
Make sure you placed translation files of the theme into the /wp-content/languages/themes/ folder with correct names (language name and woopress theme suffix, e.g woopress-de_DE.po, woopress-de_DE.mo).
If you face problems with translation, you need to be sure that your translation files are synchronized. Button Sync (Loco Translate plugin http://prntscr.com/glemdq) allows you to synchronize your translation file with pot file. Then you will be able to translate untranslated strings.
Also, don’t forget to backup all the files before any update.