Your changes in the file will be lost after theme update.
Make sure that you use latest theme and plugins versions, after that you just need to synchronize translation files (use Loco Translate plugin) of the theme and woocommerce.
Before this make sure that you placed translation files of theme into wp-content/languages/themes folder with correct name http://xstore.helpscoutdocs.com/article/30-base-theme-translation (the same for royal theme).
Button Sync allows you to synchronize your translation file with updated pot file. It means if we made any changes in template files that may affect transaltion or we added new string for the translation and you updated theme you need to synchronize your translation with updated files. Only after synchronization you’ll be able to translate new strings or strings that were changed. You may lose only strings that were changed.
Also, don’t forget to backup all the files before any update.
Please try to translate strings after synchronizing, if it won’t help, provide wp-admin and FTP access in Private Content, so we could check translation problem deeply.
