I got the git version, compiled it and the Latvian option wasn't there. Then I did some modifications to the code [0] (the link contains git patch with changes) and after recompile UI is available in Latvian.
Even after this some buttons, like Cancel and OK in Attributes and Properties dialogues stayed untranslated. I guess these are taken from other KDE libraries, which have to be translated separately, but I don't know which they are. Pointers anyone?
[0]
http://fpaste.org/48689/