Which language do you recommend learning?

Learn the one YOU prefer, not one other people could prefer for you... Do a list: pros and cons from what YOU need to do with a new language, etc... )...

Based on those details and circumstances you mentioned...oh wait.

Especially if you never learned a foreign language before (which I am guessing is the case), I strongly recommend learning Esperanto first. Not just because it's easier than any national language, but also because history has shown that people who know Esperanto learn other languages significantly faster. In effect, learning Esperanto before another language doesn't take extra time compared to just learning that other language.

If after Esperanto and an easy national language you get an appetite for languages, you can pick a "critical language" (google that) for career-opportunities

Personally, I recommend French, but whichever language you want to learn is up to you.

Every language is complex because of the accent and pronunciation.

Learn Sanskrit. It is the most scientific language.

I would recommend to take two: Spanish and Chinese.
First of all, it is generally recommended to study two languages at the same time as it is more stimulative on the mind (on one hand, you take breaks when shuffling/juggling between the two, which allows you to, sort of, refresh, and on the other hand you continue working out your brain). Basically, you are banging on the same concepts twice -- you study the word that you already know in two new different suits instead one. I would however suggest you start with the second language after one month since starting the first language. Make sure you are comfortable with the routine.
Second, you should either choose the one that you like the most (like the sound of French) or the one that you intend to use (suppose you want to read the German philosophy in the original, why would you go for Urdu?!). Since your question is not very specific in terms of why you are so passionate, the general consideration is to take the most widely spoken languages in the world. Spanish is the closest to Latin and hence is a good start for Romance languages. Chinese is also a base for Korean and Japanese.

Make a list of languages which you want to learn and answer yourself: which one has higher priority than others. Learn one language at a time.

Most European languages use the modified Roman alphabet, as used in English, with a few tweaks. The oriental languages which you mention use a totally different script system which works totally differently from any languages using the modified Roman alphabet.

Of the European languages, Spanish might be the most useful language if you live anywhere in the Americas. in certain parts of the USA there are enclaves of Italian speakers, and in eastern Canada there are many speakers of French of a dialect very different from the French spoken in France. Parts of Africa were colonies of France, so French is useful there too.

So partly it might depend ion where in the world you might want to travel to or work in.

when I think about language.... I think about the language that is used the most in this planet.   Most people know English even people in Bangkok.   Well spanish is not well used in the US (unless you live in the hispanic dense population such as LA) maybe only in Mexico and Spain.   Japan is a good language but only being used in Japan.   Then there is chinese.  Chinese or we call it "Mandarin" is used in the US, especially in most Chinatowns.   Then if you go to Taiwan and Hongkong, they do speak Mandarin.   Also Singaporean and some Indonesian can speak Mandarin.   So Mandarin is well used by many people outside China. 

I did learn French.  The grammar is almost the same as American English.  But I rarely use it in the US.   Maybe when I got to an art Museum, I can understand what it says on the "Paintings".   French is a sexy language even the swearing sounds good, LOL. 

Of course Catharine is right. As for me I prefer Spanish.It might be easier than some of the others.
It takes an awful lot of time for many years to learn a foreign language.I mean daily for many years with interaction with native speakers and usage.Don't waste your time on what you can not use.
Compare a language to a jigsaw puzzle.You need all the pieces.Just knowing some words is not enough.

If you're an American, it may be best to learn how to speak and spell English correctly before trying a different language.