Translating .deb package information
Solution 1:
The meta-information for the applications shown in Software-Center is provided by the app-install-data package. The title and short description can be translated through app-install-data's Rosetta page on Launchpad. I'm not sure if it is possible to submit a translation for the packages's long description.
Solution 2:
Here is another possible solution:
With Nightmonkey you can easily find every piece of the package description. Yes, this page links to the Launchpad translations page.
There aren't frequent updates on the official repositories, so be patient.