Sotto

Sotto is open-source language-learning software that combines CEFR coursework with private, self-hosted practice. It suits learners who want to rehearse with material from their own reading and interests, especially before speaking with a teacher or conversation partner. The free software is compelling for technically capable users, but running it and supplying AI or speech services requires ownership of the setup.

Overview

Sotto provides a structured route through grammar, reading, listening, speaking, and writing, while allowing practice outside the main progression. Advancement is tied to demonstrated mastery, so it is better suited to learners who value a deliberate sequence than to those looking only for quick daily drills. Ungated skill practice keeps focused work available when a learner needs to revisit one area.

The project runs under AGPL-3.0 and can be run, modified, and redistributed without a software fee. The trade-off is operational: you run the application, database, and files on your own infrastructure, and pay configured AI and speech providers directly. A managed hosted offering is described as planned rather than as the current model.

Key features

A per-course vocabulary and grammar memory graph uses SM-2 spaced repetition to schedule reviews. Those records also seed adaptive listening, giving review sessions a connection to listening practice instead of treating memorization and comprehension as unrelated tasks.

Personalized classes can start with an article, paper, YouTube link, or a topic of interest. Sotto levels the resulting material to the learner's CEFR course and supplies citations, making it useful for language work tied to study, work, or a particular hobby. Mock exams can follow Goethe, DELE, Cambridge English, or generic CEFR formats; their feedback helps practice, but it is not an official examination score.

Provider flexibility is unusually broad. You can configure OpenAI or Anthropic keys, use local Claude Code or Codex agents, or run local Ollama, faster-whisper, and Kokoro components. Gemini Live API is documented for real-time spoken translation, and an MCP server connects Claude Code or Codex workflows. A fully offline arrangement is possible when the language model, speech recognition, and speech generation run on your own hardware, although that places hardware and maintenance responsibility with you.

Sotto documents encrypted-at-rest per-account API keys using BYOK_ENCRYPTION_KEY. Self-hosted access uses a shared password and local learner profiles, with optional WebAuthn passkeys that an administrator can revoke. Content sent to a configured cloud provider remains subject to that provider's terms, so self-hosting improves control of the stack without making every processing step local.

Pricing

There are no paid Sotto tiers, seat charges, renewal terms, or trial period to weigh. The meaningful cost is infrastructure plus usage from whichever AI, text-to-speech, or speech-to-text providers you select. Local components can avoid provider bills, but require compatible hardware and administration.

Platforms

Sotto supports Android, iOS, Linux, macOS, Windows, web, API access, and self-hosting. The maker documents a Tauri desktop launcher for macOS, Windows, and Linux; Windows setup uses WSL2. Phones, tablets, and laptops can install the browser PWA. An iPad workbook PDF supports annotation in GoodNotes or another app, and the README describes a native iPad app targeting iPadOS 18 and later. A Rust terminal client adds audio playback and microphone recording.

Who it's for

Choose Sotto if you want CEFR structure, adaptive review, and speaking rehearsal built around your own notes, work, or interests, and you are comfortable administering a self-hosted application. It is particularly well matched to privacy-conscious learners who want local processing options and to technically inclined users who value provider choice.

Look elsewhere if you want a turnkey service with no infrastructure decisions, a formally scored certification exam, or a single subscription covering all speech and AI usage. Sotto's flexibility is an advantage only when you are willing to configure and maintain it.

Pros and cons

Pros

• Free AGPL-3.0 software: You can run, modify, and redistribute the learning stack without a license charge.
• Mastery-led CEFR courses: Progression across five core skills gives structured learners a clear route, while ungated practice prevents the course gates from blocking targeted work.
• Connected adaptive review: SM-2 vocabulary and grammar scheduling also informs adaptive listening.
• Interest-based material: Articles, papers, videos, and topics become leveled classes with citations.
• Local and cloud provider choice: OpenAI, Anthropic, local agents, Ollama, faster-whisper, Kokoro, and Gemini Live support different privacy and cost preferences.
• Broad client coverage: Desktop, PWA, mobile, terminal, and iPad workbook options accommodate different study surfaces.

Cons

• Self-hosting overhead: You must operate the application, database, files, authentication, and—in Windows—WSL2.
• Usage costs are external: Cloud AI and speech bills come directly from your chosen providers and are not bundled into Sotto.
• Practice exams are not credentials: Mock feedback cannot replace an official Goethe, DELE, or Cambridge result.
• Privacy still depends on configuration: Cloud-sent content follows each provider's terms even when the main stack is yours.

Alternatives

Duolingo is the better pick for a mainstream Android, iOS, macOS, or web experience with a freemium model and a one-week free trial, rather than self-hosting.

Busuu suits learners seeking a freemium mobile and web service with paid Premium and Premium Plus options.

Learning with Texts is another free, self-hosted choice for Linux, macOS, Windows, and web users who can run a local PHP and MySQL server.

LingQ is a freemium Android, iOS, web, and browser-extension option with a free tier capped at 20 saved words and phrases, five imported lessons, and one audio playlist.

mLearn is a free multi-platform alternative with optional cloud features and usage limits.

Innovative Language Learning offers a freemium service with free lessons and transcripts, mobile access, and paid tiers.

JapanesePod101 is a freemium Android, iOS, and web option focused on Japanese lessons and a free survival-phrases course.

Talktiko provides a freemium Android, iOS, web, and API service with a free tier limited to one language, three lessons per day, and basic text-to-speech.

Verdict

Sotto is a strong choice for technically capable learners who want CEFR progression, adaptive review, and private practice shaped by their own material. Its decisive advantage is control over the learning stack and provider configuration. Look elsewhere if you want managed convenience, predictable all-in pricing, or an official exam credential rather than self-hosted practice.