Second option, and I’ll speak Loxian unless it gets dropped for a year, in which case I’ll use Klingon for that year.

Loxian is a language made by Irish singer Enya’s songwriter, Roma Ryan. It’s a complete language, but they are the only two who know it, and they aren’t teaching it to others. Any artsy/fantasy language (such as Tolkien’s Elvish or Star Trek’s Klingon) is a great troll language, but you can learn the latter two. You cannot learn Loxian. But if you know every language, you are added to the short list of people who do know it. And Roma’s husband passed away a few months ago; she and Enya are probably not long for this world either. So once they are gone, surely nothing stands in the way of you teaching it to others (if you want to). This is what Loxian sounds like. (Yes, it sounds like both Elvish and Gaelic. Ryan crafted it after writing “May it Be” for Enya, which incorporated Tolkien’s Elvish language. That’s the song that plays at the end of Fellowship of the Ring. Writing a song with Elvish inspired her to create a language based entirely on Enya’s vocal style. Which means it would probably be harder for a normal person to learn… Enya is basically part Elf herself, or something like that.)

Of course I jest. I’d use Japanese primarily, but I’d speak in whatever language I needed to in order to communicate.