I have not mastered any language, though I consider myself to be adequately proficient at English.
I've self-taught a little Latin and a little Tengwar. I can understand Spanish, but can't speak it very well. I know Python pretty well though (enough for daily tasks). I would like to learn German and French as well as become fluent in Spanish.
I spent a couple weeks there a while back when I was traveling Europe. German people are by far the most friendly! I would totally live there if I could.
I wouldn't dare say I've mastered anything in my life, though I've gotten reasonably proficient with American English. I speak Spanish but I can't write it and I'm far from knowing it completely.
i can speak and am fluent in, english, french, spanish, and a native american dialect, i can read and understand german, but cant speak it, and have been taking japanese classes on and off for a while now
english is the only one I've mastered, I was trained as a vietnamese linguist in the army but didn't speak it well, it is a completely tonal language and my mouth just doesn't make the right sounds, I read it very well, but it was all military jargon, never conversational language
I've "mastered" Japanese (more or less). I'd like to learn Welsh before I die....