Localization

You need to put the file in the languages folder and call it es_ES.po. You can read a bit more about it here:

https://codex.www.ads-software.com/WordPress_in_Your_Language

Thanks, I didn’t know in which one, if it was in a new one under the child theme, or if I needed to recreate the libraries structure under child or add it to the theme itself. As it turned out I had to add it under themes/tonic/library/languages. Anyway, if somebody needs the Spanish translation just ask.