When the spellchecker is enabled the first time it should default to the current used locale: http://mxr.mozilla.org/mozilla/source/editor/composer/src/nsEditorSpellCheck.cpp#194 But rv = packageRegistry->GetSelectedLocale(NS_LITERAL_CSTRING("editor"), utf8DictName); fails for me and therefore en-US (as first in the list) is used always. I found that http://mxr.mozilla.org/mozilla/source/chrome/src/nsChromeRegistry.cpp#799 fails to get an "entry" for "editor" but I couldn't figure out why or which data is loaded into mPackagesHash. (I'm using a self-compiled build but I'm not sure if that makes a difference)

I probably know why that doesn't work. There is no UI for editor in Firefox (e.g. it is for Thunderbird). So there is no locale package "editor" registered for Firefox and no autodetection is happening.

(Oops, sorry for the empty comment, Firefox crashed while submitting......) So what I was writing is that the current intended behaviour is not good. Not suited to multilingual users. I think Firefox should select the spelling dictionary for a textarea based on its or the pages lang attribute. That way sites could offer an UI to change the browsers spellchecker language. There are other issues, like one textarea with paragraphs in different "language", common in East Asia for example (Hanzi+Pinyin mix, Kanji+Romaji, etc). No good solution to this exists though even in MS Word.

(In reply to Γριφεγ from comment #2) > I think Firefox should select the spelling dictionary for a textarea based > on its or the pages lang attribute. The lang attribute of the textarea maybe, but certainly not the page's lang attribute. If I'm writing an email, I want to spellcheck in the language I'm writing the email in, not the language of the webmail UI.

Closing this bug as per bug 1073827, comment #33. If you want to reopen it, please present a reproducible test case. Re. comment #0: Does retrieving the local still fail? This was reported in 2008 (!!)