RE: Translate Business Central US Version
If this is on premise version then you have to deploy the Spanish Language extension that you find in the applications folder.
This is valid for version 16.x onwards.
If this is the online version then you must be sure that you have been moved to 16.x and you will have this implemented out of the box. NOTE: we only convert the W1 strings and not the localized ones.
If you have previous version 15.x then you have to upgrade to 16.x or create your own XLIFF file.
If you are on 14.x then you could download the typical translation file (FLN) and deploy it into your environment.
I would strongly suggest you to be in touch with your CSP partner or Reseller to perform any of these tasks.