Hey Diego,
What is your language? The system should automatically switch to it if we support it. Here is a list with languages that we should support:
www.transifex.net/projects/p/compojoom-comment/
(the one that are translated to 35% have just frontend translations)
Do you see your language there? If it is there, but it is not loading in the frontend of your site, then most probably there is an invalid character and j2.5 cannot process it. (you can enable joomla debug mode + language debug and at the bottom you will see the files that are causing problems)
Daniel