Have you heard of Glottology? It is the study of how we as human beings create sounds. So how exactly do we produce sounds? If your answer is "With our mouths obviously." Your answer would be only partially correct. Because aside of all the different parts of our mouth like the lips, the tongue, the velum and the aveolar ridge we also use our throat and even our nose! Try this Speak the following aloud: "Grey english geese" now pinch your nose closed and try to say that again. It sounds very different, doesn't it? Conversely, sounds are often codified differently in different languages and even dialects. the "R" sound can is notably different in italian and RP English. At the same time the "R" is again different between RP English and a scottish accent. If a sound isn't codified in our native language we often can't even tell the difference. This makes it almost impossible to produce these sounds. So don't be to hard on yourself if you can't pronunce the german "Achtung!" or the Italian "gli". Try to listen to all the different sounds until you can tell the difference and it will become easier to produce these difficult sounds.