Copy the language files to the 'trans' directory on the SD-Card.
If the 'trans' directory does not exist, create it.

English and German languages are included in the firmware package. This directory contains files for other languages.
Language files have the following filename structure: "lang.XXXX.dat" where XXXX contains the language name.
Too use a different language go to the language section in the 'general config' of the menu on the left.