Every once in a while I see this question, and it wonders me what the big deal is. And I say again: Every (middle to upper educated) teenager in the Netherlands, but also in for example Belgium and other smaller countries studies three foreign languages in highschool. (English, French and German) Meanwhile they also study maths and geography and other stuff. Why should it be a problem???

Mostly the people asking this are from the USA, where they call a foreign language a second language pro def, since no-one would ever try to study a third or fourth foreing language. Or from Asia, but in that case I can imagine something. Any indo european language differs that much from Chinese, Korean and Japanese that you might focus on just learning one, English probably.

It is very easy

I can speak four languages

My native language is Arabic because I live in Egypt.

I speak English fluently because I'm a teacher of English

I learned French at school

I can speak Portuguese because my girlfriend is Brazilian

Good luck

@M_rk_s Your comment about "second language" terminology isn't exactly accurate. This terminology refers to the fact that speakers generally have a "first" language (L1), also referred to as a native language, that they started acquiring from birth. Of course, speakers can have more than one L1, such as when children learn multiple languages from their parents. In contrast, second language (L2) refers to any language or languages spoken other than the L1.

Sometimes it happens because you start learning one language, but you aren't passionate about it. So, you switch to another language, which becomes the new focus. It doesn't mean you aren't still learning the first language, but it is no longer your chief priority.

This happened to me. First, I studied only Spanish until I reached fluency (~10 years). When I went to college, I decided to study a language with a non-Roman script. Arabic fit into my schedule, so I studied it for 2 semesters. I enjoyed it, but I did not develop a passion for the language. Next, I studied Portuguese because I could take a Port-for-Span-speakers class as part of my Spanish major. I adore Portuguese. I'm not actively studying it right now, but I regularly use it at work and practice with friends. Now, because a friend got me hooked on Korean dramas (Kdrama lovers will understand! lol), I'm learning Korean. So, I'm currently learning Portuguese (-actively) and Korean (+actively) at the same time.

I do think that once you reach a high level of proficiency in a second language, it is easier to learn additional languages.

I find that itis okay to study more than one, if you space out the time you do each, so you can focus on each with the same intensity. I study Croatian in the morning, Romanian during the day, and French at night. This way, I don't mix up the languages. Also, setting incremental goals for yourself is great, like: finish one chapter of romanian a day, or one chapter of croatian every 5 days. Then, it is all completely organised, and you will be able to achieve more than with one big chaotic mess. I think that this is a great optimisation of time as you probably can't focus on one language that much in one day anyways, but it is possible to focus on different languages during this time, and results in much more time put to studying/interacting with native speakers.

Also, I find that each language has a particular mindset, so it gets hard to mix them up. I don't quite know how to explain this, but that's how I think about it.