Advanced Speaking Practice App

I'm looking to develop a language learning app focused on speaking practice for advanced learners.

Key features should include:
- Real-time conversation practice with native speakers
- Advanced grammar lessons integrated into speaking exercises
- Vocabulary builder tailored to advanced topics
- Performance tracking and feedback

Ideal skills and experience:
- Mobile app development
- Experience in language learning tools
- Strong understanding of advanced language concepts
- UI/UX design for educational apps