i used excel to list all keys -> langvaule_en -> langvalue_de -> langvalue -> fr etc. I then wrote a small python script which converted the key - value lists for each language into a xml file, which i then parse in unity. worked pretty good. but i did not do any fancy languages like japanese, or kyrilic languages.
usage was something like Debug.Log( "new game".localize() ); and localize looked up the value in each the corresponding language dictionary.
but i guess the one brice posted is doing a good job