Babelzilla doesn't support "install.rdf" localization.

Babel wiki show how to localize the initial description of an extension in the older way.

IMPORTANT NOTE: this tutorial is still valid but there is another way of localizing metadata in the install.rdf since Gecko 1.9 . Please read this article

The older way is still valid, but I seem to have to transcribe metadata from the older localization properties files (which are downloaded from babelzilla) to install.rdf.