Which languages do you like and/or know?
Maybe even constructed ones?
See my profile for some natural languages that I have studied more or less in detail.
I have also studied a few constructed languages (especially Lojban, Toki Pona, and Rick Morneau's Lexical Semantics which he renamed several times, for instance Latejami, Ladekwa, etc), and have (partially) constructed two myself, Lina (mostly inspired by Eurixa/Eurish) and the World Language Project (see https://the-world-language.org).
My hot tip for language learning (and/or mere enjoyment) is watching the tv series "Fuller House" on Netflix, changing your user account language to your desired target language and then changing the spoken language (I recommend no subtitles!) in the series. The series is available in many (sadly not all) of Netflix' user languages, expertly done, and is perfect for language study as it is light entertainment with everyday language spoken by different ages of both sexes. Watch it first in English to enjoy and learn the story, then have a go at other languages! Enjoy!
Just make sure you remember the (simple) Netflix menu structure when switching to a language that you cannot read. For instance, I can't read Chinese or Japanese and really had to be careful not to accidentally delete my profile instead of switching to the next language. It's quite straightforward, but still better to pay some attention.