The other day I made a handlebars helper based on fluent (available on npm). This allows localization of any template (websites, documents, etc.) that is either already using Handlebars where it can be added as a pre-processing step. My use case was localizing bits of Markdown documents before passing them to Pandoc, but there could be lots of other uses.
The Handlebars usage is pretty basic, the language and any other context variables are passed from Handlebars to Fluent along with the key to be translated, you could have data coming from one place and translations from another.
Just mentioning this here because before I made it I looked here for it and found nothing…maybe this will help some other poor soul.