Hi all.
Please read carefully if you are willing to reproduce this problem.
On Server 2012 R2, I can start a full RDP session, start IE and spell checking works without Problems. I can Switch between languages (english and german), all is good.
However, If I start Internet Explorer as a remoteApp, which is the way we want to use it, I cannot Switch between languages. Instead, when I rightclick a reddish underlined (incorrectly spelled) english word, and try to set the spell checker to english, the remote language chooser starts, but using it has no effect at all because I cannot save the changes. The remoteApp still only offers german as correction language.
This was reproducible on a perfectly clean test System as well. This used to work on remoteApp-IE11 on Server 2008 R2, by the way.
...The results? See for yourself: in this text, auto-correction has capitalized several words against my will... :(