German is a funny language. To be speaking and writing proper German you need to learn all of German, but in addition to that, you'd need Latin grammar to build some plurals, English, French and to lesser extent Italian and Turkish pronunciation for a ton of words, understanding of English idioms, since marketing and movies don't bother with translating taglines anymore, and quite a bit more. It's especially noticeable when you have little kids and have to correct them constantly when they are trying their newly acquired reading skills on billboards along the road.