I changed my keyboard language - how?

I use shortcuts and hotkeys whenever I can.
But sometimes I make a mistake somewhere and the application I'm using switches the languages, from German keyboard layout to the English layout (only the current application, not the entire OS).
I have no idea which key combination causes this and how I can get the default settings back...?

Go to Region and Language in the Control Panel, you should be able to change in there.

Keyboard Layout - Change

See screenshot:

Thanks.
But this dialogue gives me the correct settings. It's only the application that's playing crazy...
Guess I have to re-launch it, wanted to avoid that.