If you know which package the file belongs, you can just "apt-get install --reinstall <packagename>" the package, and it should restore the translation files (I think). It won't hurt to use the following command to create a backup of the files, though: Of course, if you accidentally break something else, you might have to reflash, so backing up everything is always a good idea! If .mo files are missing, your applications will still work, they will just have very weird texts in them.