Hello,
1) Download translation file you need here https://www.8theme.com/forums/xstore-wordpress-support-forum/xstore-translation-files-sharing/
2) Upload it using FTP or file manager plugin to wp-content/languages/themes folder
3) Install Loco translate plugin
4) Sync your translation https://xstore.helpscoutdocs.com/article/103-translation-files-update
5) Finish translation of missing strings because our translations are partial.
6) Go to Loco translate > Plugins > XStore core > translate core plugin.
Regards