Comment 13 for bug 303269

(In reply to comment #7)
> Make sure
> to consider HTML's lang attribute and xml:lang (whichever is appropriate) and
> as a bonus it would be nice to also select not completely specified languages
> (e.g. select es-ES for lang="es").

(In reply to comment #9)
> Or it could use the domain suffix.
>
> Example, www.example.se it would use Swedish dictionary, if I goto
> www.example.it it would use Italian dictionary.

(In reply to comment #12)
> Whatever language you end up with by looking at the lang variable etc, there
> should be a button/dropdown somewhere logical where the user can override the
> setting. After all, not all webmasters know what they are doing..

I've implemented these three points in this extension (my first one):
https://addons.mozilla.org/firefox/3414/

The problem is, I don't know how to change the language for given form fields. Hence you have to reload the page whenever the language is changed manually or automatically (at least when listening to DOMContentLoaded, which fires after the spellcheckers are instantiated). Maybe somebody can help me out here.