Didn’t really think too too hard on these, I went with the first language that came to mind when I thought about the character, hope it’s what you were looking for!
Daichi: Mandarin – Daichi’s reason is mostly practical, he knows that Mandarin is the most widely spoken language in the world, and he feels knowing it would give him an advantage in his future.
Suga: French – I totally headcanon Suga’s mom as French. Suga never really picked up the language or wanted to learn as a kid, it wasn’t until he was in high school that he took an interest in learning French.
He is also completely aware that being fluent in French, paired with his looks and charming personality, will make him even more irresistible. Boy absolutely knows that he can charm the pants off anyone he sets his eyes on.
Asahi: Spanish – He heard a group of Spanish tourists talking one time and was completely captivated by how beautiful the language was. Not completely committed to taking classes or anything, but likes to use apps and learn some phrases now and then.Nishinoya: Korean – I feel like he’s totally into K-pop and as a result he started to dive deeper and deeper into Korean culture.
Tanaka: Korean – Nishinoya had roped Tanaka into the k-pop craze with him, and the next thing he knew, his sister got into it as well. They started watching Korean variety shows together and just picked up phrases from here and there.
Ennoshita: English – Let’s be real, he spends so much time watching and analyzing western films that without even realizing it he became pretty proficient at it.
Narita: Cantonese – He seems like he’s into Bruce Lee/Jackie Chan/90s Hong Kong films???
Kinoshita: English – He’s not particularly interested into learning another language. English is part of the curriculum at school, so he’d probably keep learning it.
Kageyama: none – it’s no secret that unless it’s related to volleyball he has no motivation to learn it.
Hinata: none – His worst subject is English, and he hates studying (unless it’s got to do with volleyball), so I don’t think he’d have any interest.
Tsukishima: German – not sure if it’s because he’s blonde, but it’s the first language that came to mind for him LOL
Yamaguchi: none – He’s not really interested in learning another language, he’ll probably learn from German from Tsukishima. He’ll keep up with English from school, but not particularly interested in becoming fluent.
Kiyoko: Korean – Nishinoya and Tanaka have no idea (they would lose their shit if they found out), but Kiyoko is actually a huge k-pop fan, and has been learning Korean on her own for a few years now. In fact, she’s pretty much fluent, and would have no trouble communicating if she were to go to Korea.
Yachi: English – Yachi is interested in learning a lot of languages, but since English is already taught at school, she feels that at the very least she should be adept at it first before attempting another language.
Takeda: Japanese – and by Japanese I mean he knows all the different dialects, and even knows old/archaic forms of Japanese. I mean, the man teaches Japanese literature.
Ukai Jr: none – He doesn’t strike me as someone who would be interested in learning another language.
What a great question and these answers feel totally spot on!