from :http://www.entropy.ch/blog/Developer/2010/04/15/Git-diff-for-Localizable-strings-Files.html
First, add this to the project’s .git/info/attributes file:
*.strings diff=localizablestrings
Unfortunately you do have to add it to every project, there doesn’t seem to be a global attributes configuration file
Second, add this to your ~/.gitconfig file:
[diff "localizablestrings"]
textconv = "iconv -f utf-16 -t utf-8"