I want to translate ZenPhoto into Icelandic.

Which way is the easiest to do so?

(I only need to translate the frontend.)

Well, for the frontend, look for english sentences in the theme files for the theme you're using and translate them individually.

Real translations should come someday... :-/ Lots of work and no time though, sorry for everything being only in English.

I can translate to Brazillian Portuguese. When the time of real translations come, don't hesitate in calling me!