Everything's free for one language — except the pronunciation coach. Unlock that, and you unlock 3 or 10 languages with it.
Free tier gives you everything except the pronunciation checker. If you just want a phrasebook, stay free — that's the point. Pay when you want the coach that tells you whether you're actually being understood.
Yes. Up to 3 active at a time — swap one out from Settings, your progress in the old language is kept.
No — it sends your audio to a speech-to-text service for scoring. Everything else (Browse, Drill, Quiz, Listen) works offline.
Web works everywhere. Android app is built and available as an early APK — Play Store and App Store submissions coming soon.