https://blog.hutong-school.com/why-learning-chinese-is-not-as-hard-as-you-think/
https://cudoo.com/blog/where-is-chinese-mandarin-spoken/
https://www.languagemagazine.com/tonal-languages-use-both-sides-of-the-brain/#:~:text=Speakers%20of%20both%20English%20and,registering%20different%20pitches%20and%20tones.
https://www.youtube.com/watch?v=d9eCNdv0XMQ&t=6s
https://www.youtube.com/watch?v=G_RPTWrd_1A&feature=emb_title
https://www.visualcapitalist.com/100-most-spoken-languages/
https://www.washingtonpost.com/news/worldviews/wp/2015/04/23/the-worlds-languages-in-7-maps-and-charts/