i'm gonna uno reverse your ask actually: what languages would YOU learn if you had to learn nine more languages?
estonian because i like the idea of living in estonia and the sound of the language is incredibly pretty, aside from that i'd choose it because i think the language is just so underrated and has beautiful grammar features. it's also so unique in europe being an uralic language. uralic language power!! the only downside? it would be a pain in the ass to find estonian resources, but my motivation would make up for it
italian because it sounds aesthetic and it would be pretty easy to learn for me since i already know a romance language, and i can't pick nine difficult af languages
latvian, i know this one will be a bitch to learn because it's a completely different language family being a baltic language, but i love how it sounds, and ever since i found out it has some german sounding words it got me hooked
spanish because i like latin american culture and the language is pretty, also, it sounds similar to portuguese i'd have an easy time learning it. i would probably pick ecuadorian, mexican or venezuelian spanish, can't decide yet
finnish too, it's like estonian just more monotone. and i like the monotone. it would be easy to learn after knowing estonian too
lithuanian, i also like the sound and it's just fascinating to me how a baltic language can have some resemblance to brazilian portuguese. the slight brazilian portuguese vibes + that ancient slavic feel is just a pure eargasm. it would also be easier to learn after learning latvian since both are baltic languages
polish. it genuinely sounds like an alien language to me and making all those consonants would be so cool! i cannot imagine being a mega polyglot and not knowing a slavic language anyway.
icelandic, this would be a bit of a hassle to learn too because of the lack of resources but i love iceland and the thought of being able to talk icelandic to the locals? awesome. also it has some consonants i really like, a th sound which is cool (and rare!! and this is also one of my favorite features about the english language), it's very unique and has a beautiful sound, i like how whistly it sounds. speaking a language with noun cases (german) the grammar would probably not be as hard to learn as some others
thai, i like the cute sound of it and its vowels, plus, i cannot imagine learning nine languages and only picking languages spoken in europe except for spanish. i'd want to learn at least one asian language among nine more and thai not only has good resources but sounds very pleasing