Is there a tool to diff/merge/sort localizable strings files?

Like I said in this post, I recently found a free app called Localizable Strings Merge on the Mac App Store. It does exactly what you ask, even the sorting/beautification. And it is free. Hope it helps.

I found this tool from the Three20 project:

http://github.com/facebook/three20/blob/master/diffstrings.py

It answers my initial need in different way of what I had imagined:
it can diff between the main locale and the other locales to see what needs translating in each other locale. And then merge back the translated strings.

Note that it outputs xml files to give to the translators.

I was desperate to find a decent way to manages Localized.strings during development, when there are new strings added to the code and you don't want to manually manage all the files.

I found Localization Manager that does this quite well. It has a nonexistent documentation, but comes with a separate program for the translators. It imports your strings, keeps track of changes and exports the needed Localization.strings files back to your project.

Up till now it seems to be freeware.