I have recently installed Blesta, I have clients who only know spanish, I was able to install spanish into Blesta but for some reason when changing the language in the client account it doesn't work, neither does when creating a new client and selecting spanish as the language for that account. I was only able to set spanish under Settings -> General -> Localization, but the problem with that is that it sets spanish as the primary language for the whole Blesta program. I don't know what I am doing wrong or how to fix this. I hope someone will be able to help me with this.
I just tested this and didn't encounter that issue. One thing to consider is that if you are an admin whose language is set to English, you will see English even when you log in as a client whose language is set to Spanish. The client will see Spanish when they explicitly log in to their account (i.e. when you are not an admin masquerading as a client).
Another thing to consider is that when the language has not been completely translated in Blesta, there may be definitions that do not exist in Spanish, and so they will fallback to English.