There are a few similar threads and it looks like it should be possible but i didn't get it to work.
Bought a Samsung Tab 4 8" in the US and tried to flash the NL firmware onto it found on Sammobile:
URL to Sammobile > /firmwares/3/?download=28816
Security fail: [slb1]
Tried this with the tablet in normal mode an in usb debug mode after turning on the developer options, but that made no difference.
Since it's not that of a big deal to work with the English language and i don't want it bricked i left it at that, but i still would like to know if someone succeeded in doing this?