I would recommend you to synchronize translations.
Make sure you placed translation files of the theme into the /wp-content/languages/themes/ folder with correct names (language name and xstore theme suffix, e.g xstore-de_DE.po, xstore-de_DE.mo).
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.