As others users have mentioned, learning a lot of languages at the same time can hinder progression. It is impressive if you can pull it off but learning how clauses are put together, the correct pronunciation, the culture behind the language etc is time-consuming and requires a lot of studying and practice. More often than not, people learning lots of languages simultaneously will only be able to pick up on the basics of each language instead of deepening their understanding of a single language as a whole. So I believe that if someone wants to really learn a language, they should study one language at a time.