I finally got around to implementing support for multiple languages in my HTML / ASP.NET spell checker addin. Spell checker now detects lang attribute specified on elements, extracts ISO language and uses it to specify appropriate dictionary for the Office spell checking engine.
In order to be able to spell check multiple languages you may need to install Microsoft Office 2003 Proofing Tools or an appropriate Office 2007 Language Pack. If you never used particular language dictionary in Word, you have to try it before it becomes available in the Spell Checker add-in. Many dictionaries are installed on demand and if particular language was never activated in Word, the disctionary may be still missing. Open Word, type something in the desired language and run Word spell checker at least once to make sure it works and dictionary is installed:
Also fixed the following bugs:
1. Unable to make correction from context menu when there is only one error in the document.
2. Alt attribute is not specified as human-readable text in the rules.xml file
3. Spell checker should ignore all-uppercase strings
Download new version here: Setup.msi
Troubleshooting: see here: http://blogs.msdn.com/mikhailarkhipov/archive/2006/04/18/578529.aspx
Previous version is still available here.