Hello Younes, You can learn more than one language simultaneously, the limitation will be only on the time and effort you can dedicate to learn each language and surely in a hectic life you won't manage more than 2 or maxim 3 languages at a time. It is more challenging in fact and could facilitate the learning of the other language if they belong to the same language family such as indo european languages ( if you learning Spanish and French or Italian at the same time for example),because of many similarities in sentence structure ,grammar and vocabulary . However if you are learning Chinese and Finnish that won't be the case. Learning a language needs concentration, that is true, but that doesn't mean you can't learn more than one, a proper schedule will help you manage. You can basically learn more than one thing at the same time like studying a certain major at university and learning a language or learning more than one subject such as math ,biology etc..at school and all need concentration and mental effort, so why not 2 languages at the same time?! Learning languages in general require using similar cognitive skills and in many times similar grammatical structures as mentioned above, hence learning the one will boost the capability of learning the other. So go for it ;)

Of course you can.

Sure. :) I'm taking Spanish in college, but I'm learning Korean on the side. It's possible.

I think you need to talk to native speakers. If you get the chance to be in environment where natives speak while you have to communicate with them it will be much easier because language is something alive.

Well i think we can do that if we want but we need to work hard on that