I encouter some problems under lyx for windows to set the settings of some documents. Although, I choose french both in the preferences of LyX and in the document layout for the language settings, it doesn't seem to be taken into account anyway?
Have you also updated the babel option (in the preferences)?
It works for me:
When I change the language in Layout -> Document, all text I have becomes blue underlined because the text language won't be changed.
(This is possibly a bug.)
After changing the language manually with Layout -> Character all works fine. The language setting in the preferences is only necessary for new documents. But the babel setting is always necessary.
(I'll write to bugzilla for this.)
