I just took an informal survey amongst my teammates (including Arabic in the list), and "three out of four" developers said: Mandarin.
The interesting thing is that on my team, two are from Russia, one from China, one from Lebanon, one from the UK, and one from India. The other two are Americans.
"Someone once said that learning Chinese is "a five-year lesson in humility". I used to think this meant that at the end of five years you will have mastered Chinese and learned humility along the way. However, now having studied Chinese for over six years, I have concluded that actually the phrase means that after five years your Chinese will still be abysmal, but at least you will have thoroughly learned humility."
Classic Moser essay. I thought this would be a post about spoken languages as well, and would put mandarin at the top of the list as well. Since people are still hiring here (especially in tech related fields), I will happily take this opportunity to plug our Chinese learning product:
The ability to roll your mouse over the characters and see exactly what they mean, or just change all of the characters to pinyin on-the-fly makes it an incredibly effective way to learn Chinese.
Instead of 5 years how about you move to China and study / communicate (as opposed to having fun) everyday for half a year to the fullest of your potential, you'll be up and talking and blowing Moser's article to smithereens.
I say this because when I moved to Australia (I'm Chinese) I was speaking English in 3 month, given I was 9 yrs old - but it just shows how much more important your environment is compared to how much time you study a language (unless its a very close language).
I don't know about English acquisition, but your timeline is way off for Chinese language acquisition, even for younger children brought to China. An aggressive timeline for adults in-country would be about 2 years to conversational fluency, and less for younger kids. This is more or less the pace you see for the faster Korean learners who come to China.
I'm happy you've had a good experience in Australia. You should remember that the barriers to learning English and Chinese are fundamentally different. English requires mastery of about 100 phenomes before reading and writing skills reinforce each other and learning accelerates: the language gets more difficult as you get better. In contrast, the difficulty curve for Chinese is steep when you start but gets much easier as you improve.
Working hard is important, but equally important is giving yourself the tools to maximize learning. Someone struggling to get through Dream of the Red Chamber with a traditional dictionary is at a huge disadvantage to someone using the proper tools and resources. Learning a language is like engineering in the sense that one should use the best tools for the job, and then put in the time needed to execute.
My estimation may be biased because I am Chinese, 2 years sounds like a more reasonably good figure, which is still a lot better then the 5 years Moser claims. Also there must exist at least one language genius who can do it in 6 month :)
Indeed as you say the Chinese language is hard at the start and gets easier. In my case when I moved to Australia I forgot a lot of my Chinese even after 1 year of not reading. 4 years later I could barely read, over the holidays I was forced to study Chinese, I did nothing but read a novel, some 10 pages a day which initially made next to no sense and took almost the whole day. But after two weeks of continuous reading, I could understand a lot more, and was reading much much faster(managed to finish a 400 page book). The trick to learning to read Chinese is to get going and not stop, and skip most of what you can't understand, and gradually you will pick it up.
I would also add that if you're not seriously committed to learning Chinese, why bother? Your progress would be so painstakingly slow it would seem you're forgetting as much as you learn - I'm trying to say don't do what Moser is claiming, tackle Chinese with less than 100% with slow progress and find out it is hard after 5 years.
It is also my view that much of the difficulty is a inherently negative mental illusion that the language is hard, and that also hinders learning. If people learned Chinese as if it were playing their favorite game, instead of something inherently dry and boring (which is another argument) this will speed up the learning process.
The interesting thing is that on my team, two are from Russia, one from China, one from Lebanon, one from the UK, and one from India. The other two are Americans.