Typing accented letters from physical keyboard I use a SGH-i927 Captivate Glide (4.0.4 AT&amp;T stock rom, rooted) which has a physical US-keyboard. I frequently type in my native language which uses letters with umlauts. I know the trick that keeping e.g. 'a' pressed for a moment brings up a popup that has different variations of 'a'. However, I find that very clumsy since it breaks my typing flow. I always use the same umlauted 'a' from the popup, so the other 8 variations of 'a' are useless.

What I'm now looking for is some kind of a shortcut to 'ä'. Ideal would be the same kind of behavior that can be seen with the top row of a virtual keyboard and its embedded numbers. 

How can I make 'a' turn into 'ä' after keeping the key pressed for ~0.5 seconds?
I don't believe there is a way to do this with stock keyboard.  Try a 3rd-party keyboard app that supports language packs and transliteration for hardware keyboards.

I've personally used AnySoftKeyboard with a plugin for my native language, which worked great on my old G1's slide-out keyboard. Try to see if a layout pack for your language is available.