Test your internationalization before string freeze
Many developers seem to work in "C" locale or don't know how to test if all strings are added for translation. While you can review the code, sometimes it might not be obvious how things are presented to the user, and if strings are constructed well.
Podebug from the Translate Toolkit is made specifically to solve this problem. You can create a PO file with all strings filled with a "pseudo-translation". This should make it mostly obvious which strings are not marked for translation. Of course you have to exercise the application quite a bit, but most developers know how to do that with their own software.
Podebug has different modes for the pseudo translation, including one that will add a rich non-ASCII version of the string that still resembles the English somewhat. That also allows a developer to test for correct handling of non-ASCII information.
Apart from the normal way to use translation, you might also be interested in testing the resulting PO files with your application in another way.