We used to translate the messages using poedit or similar tools. According to my feelings the problem here is not lack of tolls, but rather lack of translators .
I'm not sure what we can do to help you with the problem?
I once considered cleaning up the Swedish translation, but decided to use it in English instead. (Apparently the poedit version available from the Ubuntu repo was rather buggy, and then even the translations which looked correct turned out not to "line up" with the phrase they were supposed to replace. That was enough to put me off the project.)
Had there been a "translation portal" along the lines spott suggested, I could have changed a word or a phrase without downloading anything and without having to submit a file anywhere. The problem is not so much the lack of translators, but rather the lack of translators wiling to accept responsibility for maintaining a translation.
The current system expects the translator to be a software developer, which obviously limits the number of potential translators available. In fact, any "professional" user (accountants etc.) would have the "domain knowledge" (terminology) required for translating the application. And any literate user would be able to fix typos and spelling mistakes.
Enabling them to do so without commitment would surely lead to better translations.