Sotto

Overview

Sotto is open-source language-learning software built around CEFR courses and private practice on infrastructure you control. It is best suited to learners who want to rehearse with material drawn from their own interests and are comfortable managing a self-hosted system. The software is free to run, but setup and any configured AI or speech services remain the operator’s responsibility.

Key features

Graded courses span grammar, reading, listening, speaking, and writing, with progression tied to demonstrated mastery. That offers a more structured path than standalone drills, while ungated skill practice lets learners work on a weak area without waiting to pass a course milestone.

A vocabulary and grammar memory graph for each course uses SM-2 spaced repetition to schedule reviews and inform adaptive listening. Connecting recall work to listening gives practice a useful through-line, though learners who want a fixed, teacher-led curriculum may prefer a less configurable format.

Learners can make classes from articles, papers, YouTube links, or topics. Sotto levels the material to the learner’s CEFR course and supplies citations, which makes it especially relevant for people who want practice grounded in their reading, studies, or work. Mock exams follow Goethe, DELE, Cambridge English, or generic CEFR formats; their feedback is for practice, not an official score.

Provider choice is a defining trade-off. Sotto can use OpenAI or Anthropic API keys, local Claude Code or Codex agents, and local components such as Ollama, faster-whisper, and Kokoro. It also documents Gemini Live for real-time spoken translation and an MCP server for Claude Code or Codex workflows. This breadth suits technically confident learners who value control, but provider configuration and any cloud-provider charges are part of the operating cost.

The application, database, and files run on the operator’s own stack. A fully offline setup keeps the language model, speech recognition, and speech generation on local hardware; when content is sent to cloud providers, those providers’ terms apply. Per-account API keys are encrypted at rest using BYOK_ENCRYPTION_KEY. Self-hosted access uses a shared password and local learner profiles, with optional WebAuthn passkeys that an administrator can revoke.

For assessment-style practice, mock exams provide feedback in familiar exam formats, but should not be treated as certification or an official result. The security policy asks for private vulnerability reports, with an acknowledgment target of 72 hours and an initial assessment within one week.

Pricing

Sotto has one plan: Self-hosted costs nothing. The AGPL-3.0 license permits users to run, modify, and redistribute the software under the same terms. There are no paid software tiers or seat and quota caps in the plan; instead, users pay configured AI and speech providers directly. Choosing local components can support an offline setup, while cloud providers may introduce separate charges and terms. A managed hosted offering is planned, but the current offering is self-hosted.

Platforms

Sotto supports Android, iOS, Linux, macOS, web, and Windows, as well as API access and self-hosted deployment. The browser app can be installed as a PWA on phones, tablets, and laptops. A Tauri desktop launcher covers macOS, Windows, and Linux; Windows setup uses WSL2, a practical hurdle for users who want a conventional Windows installer. A Rust terminal client supports audio playback and microphone recording. The web app can generate workbook PDFs for annotation in GoodNotes or another app, and the native iPad app targets iPadOS 18 or later.

Offline lessons and speech practice are supported, alongside placement testing, personalized review, and mobile apps. The documented fully offline arrangement depends on running the language and speech components on the user’s own hardware.

Who it's for

Sotto fits language learners who want structured CEFR progression and private rehearsal before speaking with a teacher, tutor, classmate, or stranger. It is particularly compelling for people who want to practice with their own material, run services locally, or choose their AI and speech providers. It is a weaker fit for learners who want a managed, ready-to-use service or do not want to handle infrastructure and provider accounts.

Pros and cons

Pros: Mastery-gated courses cover five core skills, while ungated practice leaves room to focus on immediate needs.

Pros: Source-based classes are leveled to a CEFR course and include citations, tying practice to a learner’s own material.

Pros: Local AI and speech components allow a fully offline setup, and the operator retains control of the application, database, and files.

Pros: The software is free to run, modify, and redistribute under AGPL-3.0.

Cons: Users must manage self-hosting and pay configured providers directly, so free software does not guarantee a zero-cost operating setup.

Cons: Windows desktop setup requires WSL2, adding a technical step for Windows users.

Cons: Mock-exam feedback is not an official score, so it cannot substitute for formal assessment.

Alternatives

Compare language learning apps if you want to consider a broader set of options. Duolingo is a freemium alternative with Android, iOS, macOS, and web apps, including a free plan and a one-week free trial. Innovative Language Learning offers a free lifetime account with lessons, transcripts, and mobile app access, alongside a paid Basic plan at $8 a month billed monthly; its broader platform support includes Windows. JapanesePod101 is another freemium choice for learners seeking a free entry point and a one-week trial, with Android, iOS, and web access.

Talktiko may suit learners who prefer a freemium service with a defined free allowance: one language, three lessons per day, and basic text-to-speech, across Android, iOS, web, and API. Busuu is a freemium option on Android, iOS, and web, with a free plan and paid Premium tiers for learners seeking premium learning features. Meslingo offers a free plan across Android, iOS, and web, with four skills, mini-games, flashcards, chat, video calls, community, and lesson creation.

Langua is worth considering for learners who want daily chat and Call Mode allowances in a freemium mobile and web service. TextLingo 2 may be a better fit for learners focused on articles, novels, and flashcard memorization, with a free plan that sets explicit credit, content, and quota limits across desktop, mobile, and web platforms.

Verdict

Choose Sotto if you want CEFR structure, adaptive review, and speaking practice around your own material, with the option to keep the stack offline and under your control. Its strongest reason to choose is the combination of learner-supplied classes and provider flexibility; its strongest reason to look elsewhere is the technical and financial responsibility of running the system and its AI or speech services yourself.