Sorry to post here in this section, but the Brazilian community here in the K2 forum. I want to inform you that the translation pt -BR K2 2.5 is not translating the Back End (admin)

Rename files pt-BR to en-GB and could not translate. Perhaps this translation is that translation is not available in 2.5 for K2.
I am using Joomla 1.7.2

if you are still having trouble updating the files attached to an administrator/language/pt-BR. I think it will work.