Disclaimer: full fluency, no studying required, but knowledge of the written language is not included.
I’m from the future. Go to China.
If I was a young man again, Italian. Because aside from French, it does the most for ladies; especially those that don’t understand the language.
At my current age, Chinese. Because it will come in the most useful for WWIII. After all, when China finally invades Taiwan, western powers are going to go all racist again with internment camps to hold visibly ethnic people, and not all of them will know English well. They will need translator advocates.
Going by the picture, each means successfully losing a shit ton of weight, so I’m down with either
Definitely Chinese preferably Mandarin since I already know some.
Probaly Jomon (i.e. whatever was spoken by some of the first people to inhabit Japan).