Hi Charles,
Thank you for the recommendation :)
Adding your new domain (sinchronic.es) to shopify and telling langify to use that domain for your Spanish content will allow Google and Co. to crawl your translations.
There is however 1 SEO related piece of content that currently cannot be translated: The sitemap.
The sitemap (https://support.google.com/webmasters/answer/156184?hl=en), which is generated by shopify automatically (http://docs.shopify.com/support/settings/general/where-is-my-sitemap-located), might by relevant for your SEO success and that is why I would recommend you to go with Spanish as your default/base language and translate from that one into English using langify.
Please let me know if you have any further questions :)