I have finally figured out how the localization of Firefox add-ons works when using JavaScript, so I can now begin to work on translating the add-on for as many languages as possible. The only thing I'm really missing now is the actual translations, and I'd like to wait until I have at least five other languages before I release the next version (v1.12).

If you would like to have the add-on in your language, please create a new topic for your language iin this forum along translations of the following:

"Insert multiple HTML signatures into your Gmail emails. (Replaces old Greasemonkey script.)"

I also need to translate the localization file:

# Signature Tools
editSignature = Edit Signature
editSignatureTitle = Edit the signature for the current email address.
createSignature = Create Signature
createSignatureTitle = Create a new signature for the current email address.
options = Options
reinsert = Reinsert
reinsertTitle = Reset the signature by reinserting it.

# Default signature labels for signature selector
default = Default
business = Business
family = Family
friends = Friends

# Edit/Create signature window
signatureHtmlCode = Signature HTML Code
dontKnowHtml = Don't know any HTML?
clickHereForTutorial = Click here for a tutorial
saveSignature = Save Signature
deleteSignature = Delete Signature
deleteSignatureConfirmation = Are you sure you want to delete this signature for
cancelChanges = Cancel Changes
signaturePreview = Signature Preview

# Options window
donate = Donate
donateTitle = Make a donation to help support this add-on
developedBy = by   
signaturePosition = Signature Position
aboveQuotedText = above quoted text
belowQuotedText = below quoted text
signatureLabels = Signature Labels
showReinsertButton = Show "Reinsert" Button
showReinsertDesc = show button that allows you to reinsert your signature in case it gets messed up
saveOptions = Save Options
cancel = Cancel

# Useful Links section
usefulLinks = Useful Links
projectHomePage = Project Home Page
gettingStartedGuide = Getting Started Guide
frequentlyAskedQuestions = Frequently Asked Questions
htmlTutorial = HTML Tutorial
signatureTemplates = Signature Templates
forums = Forums (feedback & Support)
knownBugs = Known Bugs
versionHistory = Version History
licenseAndUserAgreement = License & EULA
projectContributors = Project Contributors

# Promote & Support section
promoteAndSupport = Promote & Support
promoteAndSupportIntro = If you like this add-on there are several things you can do to help promote it:
spreadTheWord = Spread the word
spreadTheWordDetails = Tell your friends about the add-on. Talk about it in your blog. Suggest it to people in forums. Link to the
projectsHomePage = project's home page
wheneverPossible = whenever possible
writeAReview = White a review
writingAReviewOnThe = Writing a review on the
firefoxAddonPage = Firefox add-on page
helpsLetOthersKnow = helps let others know more about the add-on before they install it
shareIt = Share it
shareItDetails = There are lots of social networking sites out there that let you share cool things. You can use the icons below to help share the add-on with others:
submitThisAddonTo = Submit this add-on to
makeADonation = Make a donation
makeADonationDetails = Nothing says "thank you" like a donation, no matter what the amount. You can use the "Donate" button above to securely make a donation using a credit card or PayPal account.