Don't agree with post above. I have a Hero with only English available and I want Spanish.
I installed MoreLocale 2, and it has lots of different languages (Dutch among them). I choose Spanish, Sense UI restarted and EVERYTHING in my phone changed to Spanish: menus, settings, etc. The keyboard predictive text defaulted to Spanish and started suggesting words in Spanish. This means, somewhere within the OS there is a Spanish dictionary hidden and MoreLocale made it available.
The problem is that English is still the only option available in keyboard input language so I can switch to English but can't switch back to Spanish unless I restart Sense UI, which takes a couple of minutes so not a very practical solution.
Still looking for an easier way to do it so please help.