I downloaded the latest version of pt_BR (brazilian portuguese) and install in the locale folder, I choose brazilian portuguese for the language in the gallery options, I have the gettext() enable on my server, but the interface of the theme (i´m using the default theme with dark option) doesn't be translated.
I download the Poedit and check if the zenphoto.po was correct. The words next, prev, search, and the name of form fields, was correct translated in .po file.

What happen? Why the translation doesn't work?
What can I do?

The brazilian portuguese translation has been done for Zenphoto 1.1.6 as the ticket where you download says and not been updated since. Since gettext checks for line numbers where the string to be translated is it might be that changes made recently affect that. One line change from for example line 1 to line 2 can cause that.

You can either wait until the original translator updates the file or just do it your self. We would appreaciate that. In that case be sure to read our translation tutorial and consider joining the google translators group.