Hello, Cristina
Thanks for using XStore.
You need to translate the parent theme. The child theme should be translated only in case you added custom code in child theme that includes localization functions. To prevent the translation loss after updates, 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-es_MX.po, xstore-es_MX.mo).
Provide wp-admin access, so we can take a closer look at your setting.
Kind Regards,
8theme team