In the next nightly build multi-language support is added for Kobo!
The actual translation of koreader in languages other than english is done at
Transifex.
Today I added Dutch language support for koreader. However, not all messages for all languages have been translated and reviewed yet.
Anyone who is interested can head over to Transifex and help. You can review the translations already done, fill in the untranslated gaps and
request other languages for koreader. (I did this for Dutch today and it took me 3 moments during the evening to translate the 200 or so strings. That's also the reason for the need for reviews of course!
)