Maybe this is more of a suggestion, but I would find the interface much easier to use if there were hotkeys for "record" and "stop" and there should be a way to type the non-english characters with the keyboard. Or is this already possible?
if you happen to use a mac, the Umlaut is 'option u' then the vowel. or the vowel than a 'e' also works. no idea about the record stop buttons.
Don't know about short cuts for record and stop. But if you can get the focus to the record area, say by clicking on it or by pressing the tab key, the Enter key does both the jobs (record/ stop). As for the "non english" :) keys, there must be a way for you to change the keyboard layout in your operating system. In Win7 for example, you go to Control Panel -> Region and Language -> Keyboards and Languages -> Change Keyboards and then choose the DE keyboard. The trick is then to remember which key is where (since the hardware is going to be the same).