Press and hold for accents does not work everytime I am a German User, but i am using a US Keyboard and the US Extended Keyboard Layout. Sometimes I need to use German Umlauts, and I usually rely on the "press and hold for accented characters" feature of OS X.

However, this is not always available. I cant seem to find a pattern in this behavior. Sometimes I log in, and it works flawlessly, sometimes it doesn't work at all and just repeats the character I press for a long time. 

I switched to different keyboard layouts (US, US Extended, US International PC) and different "Preferred Languages" in the "Language and Region" settings. 

I also tried the defaults write -g ApplePressAndHoldEnabled -bool true setting, but also no luck. 

I have the same problem on different Macs; at work and at home.

How do I configure this feature correctly?
When it stops working, does ps -ef|grep PressAndHold include a line for /System/Library/Input Methods/PressAndHold.app/Contents/MacOS/PressAndHold? If it doesn't, try to run open -a PressAndHold. Or if it does, killall PressAndHold;open -a PressAndHold might also be worth a shot.

You could also try to delete ~/Library/Preferences/com.apple.HIToolbox.plist. Normally defaults read com.apple.HIToolbox should show com.apple.PressAndHold under AppleEnabledInputSources and AppleSelectedInputSources.