I voted En-to-Jp, but also think the 3000 - 5000 words cap will make it almost useless.
It's generally accepted that we need at least 10,000 words (N1 level) for basic reading in Japanese (unlike English, which 5000 will do), which is just equivalent to the Grade 3 level in K12! 5000 words for paid user is just at the level of 6-year-old of native speaker, far away from enough to do anything with it.
I hope that JP course can cap at N1 level (N2 for free user maybe?), while other languages will also get vocab size increase in the future (I am doing En-to-De, it would be nice to get to C1 level, ~10000 ).