Hello,
1) Go to Settings > General and select your language – http://prntscr.com/poca4x
2) Make sure that translation files have correct names – your language name and xstore theme suffix, e.g xstore-de_DE.po.
3) Go to Loco Translate > Themes > XStore > Select your language > click on Sync btn https://xstore.helpscoutdocs.com/article/103-translation-files-update > Save translation. Then you will be able to translate untranslated strings. Before checking the frontend, do not forget to clear cache to ba able to see changes.
You need to translate XStore Core plugin also. This article will help to sorted out with the translation of WooCommerce plugin – https://docs.woocommerce.com/document/woocommerce-localization/
Regards