Best architecture for seamless Bilingual TTS? (Azure / English + Korean) [D]

Hi guys, when building a language learning app (React Native/Expo frontend, Python backend) and I’ve hit a frustrating wall with Text-to-Speech. I need the app to read sentences that mix English instructions and Korean examples (e.g., "To say hello, we use the phrase 안녕하세요."). Since native pronunciation is critical for a learning app, I'm struggling to find a solution that sounds natural. I'm currently using Azure Cognitive Services, and I'm stuck between two bad options: Approach 1: The Multilingual Voice (en-US-AvaMultilingualNeural) The Good: Seamless reading, zero pauses mid-sentence.