Hm, one I can think of in Swedish is the adjective scared. It only works when you put one of our two words for "a" before it(got no clue what they're called). The Swedish types are either en or ett. Got no clue about the rule for when we use which, since it seems totally random. En katt, ett marsvin(a cat, a guine pig). Ett hus, en bil(a house, a car). Perhaps some Swede who actually paid attention in school knows.
Anyways, you can say "en rädd människa(a scared human)", but you can't say a scared lion since the word scared doesn't bend right. The worlds that magically appear in your mouth becomes "ett rätt lejon", which translated to English means "a correct lion".
To bypass it you gotta change it to "ett lejon som är rädd(a lion that is scared)" or change the word to "skrämt" which is another word for scared. It's mainly used as a verb though.
Hopefully someone understands. I lost myself a few times.
Can also add, like others have, my minor issues with the English language:
I can't pronounce the double t's without struggling. Letter for example sounds the same as leather out of my mouth. Got plenty of double t in Swedish, but I've never had any issues with those.
Was quite annoying trying to give a tourist directions to the building with the golden letters.