Hello, Cristina
Read this article – https://xstore.helpscoutdocs.com/article/30-base-theme-translation We would recommend you use the Loco Translate plugin.
Go to this page https://www.8theme.com/glotpress/projects/xstore/xstore/es-mx/default/ and click on Export, rename the file to xstore-es_MX.po, upload it into /wp-content/languages/themes/ folder , then you need to synchronize translation – https://xstore.helpscoutdocs.com/article/103-translation-files-update
Kind Regards,
8theme team