We are using Transifex to translate the web interface:
https://www.transifex.com/projects/p/urbackup/
Create an account and request a language group creation. I'll try to approve your request as fast as possible!
There is another method where you can see the translated web interface directly:
Once you installed the server you will see a translation.js in the www directory.
...
If you are starting with the english version, don't forget to translate the strings that have no english translation (because the strings themselves contain the translation). Those are all starting with "t". You'll find them e.g. at the German or Russian version.
Please create a ticket in our issue tracking system once you are starting something, so that work isn't done twice, per chance.
Currently being translated are: