Yarrow is the best language learning application with the highest score of 400 points. The only problem is that it does not exist yet.
1) The most popular apps are not «language-specific». I can not analyze 500 apps because I do it for free.
2) Did you try Skyeng (not SkyLAng) yourself? It's paid, right, but it's good.
Excellent app must contain voices, texts etc or you need to install several apps and this will be less useful.