Here are a few ideas and changes . . . though I really don’t know how to render your title sentence. . it does not make sense in English - is it a saying in the Czech Republic?
As many languages you know so many times you are a human
What languages do you currently know apart from your native language/tongue: English, Spanish, Chinese or German? If you can speak at least one of these languages, it is certainly sure, that you will be able to understand and communicate with people from other parts of the world. You will have some idea of the difficulties and advantages of learning a foreign language.
I believe that one of the main advantages of speaking a foreign language is that you can communicate with other people, for example when on holiday. It is certainly useful for business communications and furthermore, you gain respect for another’s culture.
On the other hand, it takes a long time to master another language. The major drawback could be that language courses are often expensive and sometimes it is really hard for students to stay motivated.
In my opinion, it is beneficial/useful to be competent in another language. It is important for young people to not give up learning a foreign language, to continue, in spite of it being a challenge.