How to enable right ALT modifier key for german Umlauts?

Hi,

I'm using an US keyboard for coding witg KEIL uVision V4.24.00.0 and trying to get the right ALT modifier key for Umlauts working.

This does work with most other applications.

But in uVision, all it does, is to open the window menus, as does the left ALT key.

Is there any way to change this behaviour?

Best Regards,

Marc