Coursera course "The Bilingual Brain"

https://www.coursera.org/learn/bilingual

> This course explores the brain bases of bilingualism by discussing literature relevant to differences in age of initial learning, proficiency, and control in the nonverbal, single language and dual-language literature. Participants will learn about the latest research related to how humans learn one or two languages and other cognitive skills.

I took it and it is in line with my personal experience (German native, English and Russian second, a tiny - and by now mostly forgotten - bit of French, Arabic).

The TL;DR of the science according to that course: No it is not more difficult. The only thing that is different is the very basics of how you form and recognize sounds in their most basic form. You learn those in very early childhood. Late learners will use different areas of the brain, partially, but they won't be worse, except they'll have an accent especially if the sounds in the new language are very different from the ones you are used to.

How long does it take you to learn your native tongue? It's years for the basics, well over a decade to become proficient. What makes it seem like less of an effort may be that you don't have an choice when you are 3 years old about what else to do with your time. You MUST learn the language.

By now, English is just like my native language to me as far as listening is concerned. If I have to speak it gets a little bit more exhausting compared to my mother tongue if I have to do it for long stretches. I never, ever have to reach for the German word first, except when I really don't know the word in English: For example, there are sooo many special words about craftsmanship staff or machinery that I learned because I did a lot of that stuff as a child, but as an adult I only ever needed "daily life English" and "IT English", so overall I still know a lot more words in German simply because I never need(ed) them in my English-language life.

In Russian I feel completely at home and comfortably "understand" each and every word even when it's spoken very quickly - but I have no idea what they say. I understand the words on the "sounds" level, and I also have a feeling for the grammar, but since I rarely ever actually used the language my internal dictionary doesn't have nearly enough words for a useful conversation. However, I found/find it interesting, this dichotomy, that on the one hand I feel completely at home with that language on a very low level (sounds and grammar), and yet I cannot actually do anything with it because on a higher level the words and their meanings are missing.

I stopped being interested in learning more languages when I realized that I'm plenty busy just perfecting my knowledge of English, the one language I actually use. When I was proficient reading Stephen King novels and daily papers I picked up "The Lord of the Rings" and for the first 50 pages or so I had to consult a dictionary about ten times per page. Same when I read The Economist instead of daily newspapers, so many new words.

I found that I was no longer interested in small talk, something you can do after a relatively short time of learning a language, I was interested in deep(er) conversations, but learning enough of a language for that kind of conversation takes much longer. But how many deep conversations could you have in your native tongue at the age of ten? Okay, maturity also factors in, but overall I see no basis for a claim that learning languages becomes harder per se. As an aggregate effect, sure, I just pointed to a few reasons myself after all.