Created attachment 347949 [details] A mail with <span lang=".."> When typing a message, I sometimes switch language, for instance when I type in my own language (dutch) and quote some other text in english. Now, all those English words are not recognized by the Spelling Checker, until I switch language to English, but then the Dutch words aren't recognized. It would be better to be able to specify the language in the message, just as it is possible in Word of OpenOffice. You could maybe use DOM for that, or HTML <span lang="nl">..</span> elements and make Spelling Checker recognize them and switch dictionary. This would be very useful for Thunderbird (and Seamonkey), but could also be useful for Firefox in text fields, when editing some wiki or other page. The e-mail GUI should have an option to change the language in a message, or for some selected text and the spelling checker should change dictionary when it sees such a marker.