I'm developing an add-on for Firefox and I now wish to localize the name and description of the add-on itself, as visible to the user in the Add-ons Manager menu.
However, the guides I've seen online only seem to mention preferences in package.json and nothing about the name of the add-on or its description. I have tried to apply the suggestions for preferences to the name/description fields and haven't had any success - it will always appear in English.
Is localization of these fields even possible?
There is currently no way to do this from package.json. Read bug 661083 for more details.
However, there is a workaround: Manually edit install.rdf to add em:localized properties.
To do this you'll need to use the SDK to package your app into an xpi file. Then open the xpi (it is a zip file) and you'll see install.rdf in the root of the directory.
The MDN article Localizing extension descriptions describes what structure the em:localized properties needs to have.