This bugs serves as the continuation of the discussion that started here: https://groups.google.com/d/msg/mozilla.dev.platform/Et02D8Mk2d0/7u7bkvTyLQAJ and has been continued in private messages. Basically the suggestion is to detect the language as one types into an editor text field (textarea or <div contenteditable>. I would suggest the following user interface for that: In Firefox in about:preferences#content we currently have: Languages Choose your preferred language for displaying pages Underneath I suggest to add: Spell Checking [ ] Spell check based on the website's language (default) [ ] Detect automatically [ ] Always use ___ (dropdown to select) Note: An all cases a site specific language can be chosen. The option "Always use" is what was asked for in bug 1073840. We might as well implement this at the same time. On "Languages" in the context menu I would add two items under the list of languages so the user doesn't have to visit the preferences: [ ] Detect automatically [ ] Always use selected language. It goes without saying that "Detect automatically" and "Always use" will only be offered, if the there is more than one dictionary installed. One note of caution: The French dictionaries come in a pack (fr-modern, fr-classic, fr-reform and fr-classic/reform - with few differences), so the automatic mechanism would have a hard time to detect the correct one. If would switch between them while the user continues typing. The same is true for various versions of English. If the user starts typing: "My favourite (en-GB/en-AU) color (en-US) is green" than the automatic detection might switch between dictionaries, which might be a little annoying.

Regarding the French variants, couldn't a user "hide" some variants, or perhaps one could be selected as default answer for when the language guesser says "French"? Typically guessers don't do too good a job on very closely related languages, but they're still very useful for e.g. French vs English, so one could push the finer details of the problem into the UI. I see https://dxr.mozilla.org/mozilla-central/source/browser/components/translation/LanguageDetector.jsm mentioned in the original thread, so it seems like the groundwork is in place already.

I failed to convince many of my friends living in France to try out Firefox again because of the lack of language detection for spellchecking. Some of them writes in 4 different languages on a daily basis.

Mass bug change to replace various 'parity' whiteboard flags with the new canonical keywords. (See bug 1443764 comment 13.)