Setting the lang attribute on a textarea element or document doesn't always result in the correct spellcheck language being selected

[Chris Coulson]

This was picked up by editor/composer/test/test_async_UpdateCurrentDictionary.html chrome mochitest failure. The test was introduced here http://hg.mozilla.org/mozilla-central/rev/8f48c49425ab , but I suspect the issue is not actually a new one. The test log looks like:

10543 INFO TEST-START | chrome://mochitests/content/chrome/editor/composer/test/test_async_UpdateCurrentDictionary.html
10544 INFO TEST-PASS | chrome://mochitests/content/chrome/editor/composer/test/test_async_UpdateCurrentDictionary.html | Inline spell checker should exist after focus and spell check
10545 INFO TEST-PASS | chrome://mochitests/content/chrome/editor/composer/test/test_async_UpdateCurrentDictionary.html | Current dictionary should not be set yet.
10546 ERROR TEST-UNEXPECTED-FAIL | chrome://mochitests/content/chrome/editor/composer/test/test_async_UpdateCurrentDictionary.html | UpdateCurrentDictionary should set the current dictionary. - got , expected en-US

The issue is that the language is set to "en-US", which doesn't correctly map to "en_US" (the dictionaries are keyed by filename). I'm sure a workaround for a similar bug has already been added elsewhere in Firefox

[Chris Coulson (chrisccoulson)]

The following test failures might actually be caused by this bug:

bug 1158836
bug 1158866
bug 1158869
bug 1158870
bug 1159073
bug 1194440