> In Germany if you don't start accelerating when the light turns yellow, the guy behind you will start honking.

Don't generalize. Usually, you have some seconds until the driver behind you will honk. I normally count "21 - 22 - 23", then I honk if there hasn't been any reaction (restarting the engine, pressing the brake pedal, etc.). But your mileage my vary.

Maybe it's area dependant, in my city they definitely honk in under a second.

German car driver here. I don't use it as signal of anger, but as hint, that the driver in front has to refocus on the traffic again. (Others may still angry-honk of course)

I realize in Germany yellow comes before green (and not after, like America). But it still reminds me of this Simpsons clip;

https://youtu.be/QR10t-B9nYY

It comes before and after.

Green -> Yellow (go if you're still at a speed that stopping would be dangerous) -> Red -> Red & Yellow (get ready) -> Green

They do this in Tijuana too (in this case honk when the red is about to turn green). They clearly are not giving you a chance, you are always just presumed to be sleeping.

Anecdata. I can't remember that this happened to me more than like twice, and I've been driving here for 18ish years...

As they should, get a move on (not you specifically of course ;))