I today managed to convert current translation data to gettext format. Thanks to conversion to gettext, we can now use many standard tools to translate Gammu. One of such tool which is already used for Wammu is Pootle.
I added Gammu po files to my installation and you can now translate online! Currently all languages are open, but if somebody want to manage some language on his own, feel free to write me. Also any requests for adding new language should go to my email.