What was in the name tag was a description of the plaque, but not a proper name.

All the "inscription:translation:es:description:XX" tags are  nothing else than the source of the translated transcription, so they should be in a source tag.

The -t- syntax is a standard also outside OSM for literally transformed text from one language to another.

In general, translations should not be in OSM - we're not a dictionary. On the other hand, one translation from Latin to the local language can for sure be helpful to understand what the POI is. 

If you prefer having the translation in "inscription:translation:es" instead, this is fine with me - although I'd prefer a 'description' tag.

I didn't move the Catalan description to a Spanish tag - there's only a Spanish translation and it's source tag, which is in Catalan.