Why not add signs in Zombies mode explaining the purpose of the chests, but written in Spanish instead of English, so that new Spanish players can understand their function?
For example:
weapon chest / cofre de armas
This way, Spanish players will know where to buy weapons. or add a tutorial map that explains how to play
Regardless of which is the language,
Terraria has a limit of characters per names/sign, adding multi language text would probably not be feasible,and in general would be just a lot of text clutter
As well, that would add the requirement to add localization code (Code that can change the language) because a lot of the texts (such as the chest text that you have pointed out) is generated from code
and in general, that would add the requirement of many people to learn spanish,which would essencially make everything harder to do/take longer
and would be esssencially forcing staff members to handle with spanish texts, which is not a good thing
Even if that was not a problem, There is not really a big enough spanish talking playerbase to do something like that