Version on extras is only finnish (0.5.0).
So you must wait.

Version on extras-devel (0.6.8) has finnish+english+german. They are all bundled with same package (automatically installed) called *-fi, do not let it confuse you.

It uses (should use) same language which your device uses ($LANG).

This language affects only to mentor (bear). Language of songs is user-selectable on song selection menu.

Beware of extras-devel version, it uses too much resources and may not work fast enough to be playable at all! Volunteer to test devel-version with overclocked device? ("How much too much we are using/wasting processing power?")