language learning3 vocabulary builder3 admob integration2 admob ready1 android app source code1 android source code1 android template1 child-friendly app1 duolingo clone1 early childhood learning1 edtech app1 education app template1 educational app1 educational games1 english learning1 english learning app1 facebook ads1 gamification1 grammar app1 kotlin1 kotlin template1 language exploration1 language quiz1 learning streaks1 material design 31 mvvm1 offline learning app1 preschool education1 pronunciation app1 reskin ready1