I think the hardest is to learn the first second language. Some people acquire languages and vocabulary easier than others. I belong among those "unlucky" ones, who need to put an extra effort and I mean tonnes of extra effort! I had been learning English for 12 whole years at school and it got me guess where? Nowhere! And trust me, I had the best school with teachers from all over the world. At that time Italki did not exist and there wasn't even a Facebook. I did not wanted to waste my 12 years of hard work and booked a one way trip to England before I finished my education.  I would say, I became fluent in English in less than a year, but without any further studying. Although, it took me an additional 4 years to feel really comfortable in any kind of situation and with any accent... Scottish, Irish.  But I prefer not to understand Cockney one :) 

I have started learning Mandarin 5 months ago and I seriously doubt, I will become fluent in less than 4 years. So currently, I am studying for 3 hours every day (2 hours audio, 1 hour writing). If I had chosen Spanish rather than Mandarin, I think I would have become fluent with this routine in one or two years. 

Now everybody says... Yes, it is easy for you, because you are GOOD with languages! Hello?! 真的吗？ 你开玩笑吗？！我不觉得， 我的记忆不好 !

The toxic system of learning languages in our schools is there to blame. I am not gifted, neither can I learn a new language, just by sitting at a boring lessons at school which concentrate on grammar more than on actual communication. 

I think 5 years for a first time learner is a very achievable goal for almost anyone. The smart cookies would be probably able to do it in a half of the time. 

And then any other language around 2 years, unless you learn the new writing system with it. 

Please do not grill me, my English is still far away from perfect :D

What a great topic to discuss :) I would love to write another book, however I feel a bit stuck at the moment. It is not easy to write in a language which is not my mother tongue and which I learned as an adult. I get frustrated very easily. I started to write my first novel last year, but got really busy and I have not written a single page since joining Italki and starting to learn Mandarin. Should I blame this site? :D The first book was quite easy to come up with in 2015 and it did not take long to write as it was only a collection of poetry. Although, I have plenty of material for a sequel and love to write simple rhymes, this is not my priority now, it is not cheap to edit and illustrate it. I need to finish the novel first and then I will decide. The time is the essence and when I don't have any, the inspiration does not come. I need to work less and write more,  however books don't put the food on the table, at least... not on mine :D. Good luck with your writing and keep us posted.