Portuguese Language is installed, but there's no change in the backoffice (still in english).

There's also a question regarding the label's shown in the front end that's probably related with the language question: it's beeing displayed the constants instead of the values (K2_WRITER_BY, K2_AUTHOR, etc.).

Best Regards.

You have language overrides which are created for english language. Just copy/create them for your language.