Corrections

Since I was raised monolingually I had to learn every language from scratch expect of my mother tongue German, of course.

Regarding foreign languages I'd concern myself to be highly skilled cause I've already studied 8 different ones.

The advantage of a multilingual education in your childhood is that you'll probably never forget the languages at all for your whole life, even if you don't use them for a long time.

However if you start to learn a language as a adult you will totally forget it after haven't practised it for years.

Therefore I have to focuse my daily live on the repetition of every single language.

Furthermore I don't believe that it would really be doable to approach a native level in a foreign language without having lived abroad as well as having learned it since your early years.

Of course there might be some genius who reaches this goal from time to time but its not usually like this.

To sum up this text, you really have to practise on a regular basis, otherwise you'll get a lack of motivation realizing that you don't speak a language as well as you did some time ago.