We would like to translate whole frontend and partially backend using CSV files. Maybe to publish full language package for Finnish what is working with CE 1.9. But we need help to choose best way to translate these files. Is there extension for it or should we use Excel or what?
Either using excel or a text editor is usually fine to edit the translation files.
My advice would be to start with an extension for your language / area and then work from there.
Here's a link to all the language packs on connect..
Finnish (Finland) Language Pack is working only on 1.6 version and last update 2012-02-05 as a beta version so i think its easier to make brand new than update that existing?