I can't say for sure because I have an English keyboard but...there's a feature in MacOS System Preferences that might help. Go to System Preferences, and then Language and Text, and then Input Sources.
Check the box next to U.S. English or British (try both if necessary). Then check Show Input Menu In Menu Bar.
Now you'll have a little flag next to the clock. Click that and switch the language before you run CoH - or during, but you'll have to use Cmd-Enter and go to Windowed Mode to see the flag while you're playing.
Manga @ Triumph
"Meanwhile In The Halls Of Titan"...Titan Network Working To Save City Of Heroes
Save Paragon City! Efforts Coordination
Well, I guess that is one way to solve it. Thanks for the idea.
The real problem is that Cider does not seem to recognize the Alt-key.
I must accept that Cider has a lot of funny "features" like not supporting Alt or more than three buttons on a mouse 
By the Alt key, do you mean the one that says "Option" also or are you using a Windows keyboard (one with an Alt and a Windows key)?
On Windows keyboards, translation environments often reverse the Windows and Alt key (so Windows is Alt, and Alt is Cmd), so that might be your problem.
Manga @ Triumph
"Meanwhile In The Halls Of Titan"...Titan Network Working To Save City Of Heroes
Save Paragon City! Efforts Coordination
It's the Option key (mac keyboard).
The Command key works as expected, at least for Copy/Paste.
I cannot create special characters like '$', '[', and similar. This makes macro creation and manual power description in chat ("[Brawl]" for example) a hurdle.
The work-around is to Cmd-Enter and open a text editor to enter the character and copy/paste it back to the game.
Has anyone who has this problem found a way to solve it?