Learn any language by speaking- language harness design

Learn any language with an AI tutor supporting 88 pairs. Discover how to balance AI and logic in a mobile-first language learning harness.

OpenAI realtime speech-to-speech Swift Codex Cloudflare Durable Objects iOS

Overview

I built an AI language tutor that supports 88 language pairs out of the box. It uses the OpenAI speech-to-speech model under the surface. I developed my own language learning harness that handles language assessment, lesson planning, personalization and memory.

Plus I built this app entirely with Codex running on my own mobile phone, no laptop work, not even to list the app on the App store

I’ll demo a live iOS app running on my phone - I can likely mirror the phone during the demo

Links

https://glottie.app/
Glottie is an iOS voice-first AI language tutor offering adaptive, private conversation practice across ten regional dialects.

Tech stack

OpenAI realtime speech-to-speech

OpenAI's Realtime API enables low-latency, speech-to-speech conversational experiences by streaming audio directly to and from GPT-4o without intermediate text steps.

The OpenAI Realtime API delivers natural, multimodal voice interactions by bypassing the traditional, high-latency pipeline of separate transcription, reasoning, and synthesis steps. Operating over WebSocket and WebRTC connections, the API streams audio directly to and from GPT-4o models to achieve conversational response times (often under 300 milliseconds). Developers get native support for voice activity detection, interruption handling, and function calling. This makes it straightforward to build responsive voice agents, real-time translators, and interactive customer service systems.

https://platform.openai.com/docs/guides/realtime

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Swift

Swift is an open-source, compiled programming language: it's fast, safe, and expressive for building apps across all Apple platforms and beyond.

Swift is a powerful, multi-paradigm language, originally launched by Apple in 2014 to replace C-based languages for their ecosystem. It was engineered for performance, leveraging the LLVM compiler to produce lightning-fast, optimized machine code. The design prioritizes safety: features like Automatic Reference Counting (ARC) and explicit handling of optionals eliminate entire classes of common bugs (e.g., null pointer dereferencing). Now open-source under the Apache 2.0 license, Swift (current stable version 6.2.1) is the primary language for iOS, macOS, and watchOS development, with growing adoption for server-side and Linux applications.

https://www.swift.org

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Codex

Codex is OpenAI's autonomous AI software engineering agent: it executes full development tasks in a sandboxed cloud environment.

Codex is the advanced, cloud-based software engineering agent from OpenAI, built on a specialized model like `codex-1` (a fine-tuned version of `o3`). It operates on an asynchronous delegation model, allowing developers to assign complete tasks—not just receive suggestions—via the ChatGPT interface. The agent works independently in a secure, isolated cloud container provisioned with the user's GitHub repository and environment. It reads code, writes new features, fixes bugs, runs tests, and drafts Pull Requests (PRs) for review, significantly accelerating the development lifecycle. Access is provided through ChatGPT Plus, Pro, and Enterprise plans.

https://openai.com/codex

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Cloudflare Durable Objects

Globally-unique, single-threaded serverless instances providing strongly consistent state for distributed applications.

Durable Objects are unique Cloudflare Workers: they combine compute with transactional, strongly consistent storage. Each Object instance is globally-unique by ID, acting as a single-point-of-coordination for multiple clients, a critical feature for real-time applications like chat or collaborative editing. The platform guarantees only one instance exists worldwide for a given ID, ensuring strong consistency without the complexity of distributed locks. They scale elastically, support WebSockets and the Alarms API for scheduled tasks, and offer SQLite-backed storage options, effectively delivering stateful serverless at the edge.

https://developers.cloudflare.com/durable-objects/

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iOS

Apple's proprietary mobile operating system: powers the iPhone with an intuitive multi-touch interface, robust security architecture, and deep integration across the Apple hardware ecosystem.

iOS is the foundational mobile operating system, first unveiled in 2007, that drives the iPhone and serves as the core technology for iPadOS, watchOS, and tvOS. Its user experience is defined by direct manipulation via multi-touch gestures (tap, swipe, pinch) and a consistent, streamlined interface. Major versions, such as the current iOS 26, are released annually, bringing new features like Apple Intelligence and enhancing core services. The platform is supported by the App Store, which hosts over 3.8 million applications, reinforcing its market position and developer commitment.

https://www.apple.com/iphone/

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Learn any language by speaking- language harness design

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