Something I find really counterintuitive, and didn't believe till I tried it: learning more than one language at once seems to make acquisition easier for the main language I'm learning? Like, I don't have a spreadsheet or anything, but my main language learning is French right now, and it feels like if I start the day with a little basic German I score higher on the French. All I can figure is there's some brain part saying "okay fine, we're doing languages now." Like a warm-up?