Build your own Duolingo.

# Build an original app inspired by Duolingo

You are an experienced mobile product designer and mobile engineer. Build a working, polished MVP from the brief below. Implement the core journeys end to end; a static mockup is not sufficient. Inspect the current environment, make sensible implementation decisions, and get started. Ask a question only if a missing answer genuinely blocks implementation.

Starting platform: iOS / Android. Explicit customized Product & audience and Tech stack requirements take precedence over this starting target.

## Product & audience
Build an original native language practice app called Wordtrail, inspired by Duolingo. It is for beginners learning one small, original vocabulary course. The primary journey is choosing a lesson, answering a mix of exercises, getting useful feedback, and returning to review mistakes. Deliver installable iOS and Android projects with real persisted learning progress, rather than a lesson screen in a mobile browser.

## Design
Create an original warm, illustrated interface with a lesson map, large answer controls, visible lesson progress, and a quiet review tab. Use your own characters and wording. Make correct and incorrect answers understandable without color alone. Respect safe areas, system text scaling, screen readers, and reduced motion; keep the software keyboard from obscuring an answer.

## Features
1. Course and lessons: bundle a small original course with ordered units, vocabulary, translations, and explanatory hints. Let learners preview objectives and resume their current lesson. Separate learning content from presentation so another course can be added without changing widgets.

2. Exercises: support multiple choice, word matching, and typed translation with explicit accepted answers. Normalize case and whitespace without accepting unrelated answers. Reveal a short explanation after checking; avoid grading while the learner is still typing.

3. Progress: persist each answer once, derive lesson completion and earned points from actual attempts, and unlock the next lesson using a documented rule. Save an interrupted lesson so switching apps or process termination cannot erase completed answers.

4. Review: enqueue missed vocabulary, prioritize due items with a simple documented interval schedule, and remove an item only after a successful review. Provide an honest empty state when nothing is due and let learners browse learned vocabulary.

5. Daily routine: show a local-calendar practice streak, allow a modest daily goal, and offer opt-in reminders. The app remains fully usable if notifications are denied. Finish lessons and review cached content without a network connection.

## Tech stack
Use Flutter and Dart for a new project, retaining a suitable existing native project if one exists. Include both iOS and Android project directories, a maintained SQLite persistence layer, and platform notification adapters. Keep answer evaluation, scheduling, and calendar rules in testable Dart modules. Do not substitute a WebView or PWA for the native targets. No account, language-model API, microphone, or remote grading service is required for the initial bundled course.

## Data & behavior
Course; Unit; Lesson; Exercise {id, kind, prompt, choices, acceptedAnswers, vocabularyIds, explanation}; VocabularyItem; LessonSession {id, lessonId, currentExercise, state}; AnswerAttempt {sessionId, exerciseId, answer, correct, checkedAt}; ReviewState {itemId, dueAt, intervalDays}; PracticeDay {localDate, timeZone}; ReminderSetting. Use stable content IDs and a content version, enforce one committed answer per exercise/session, and migrate the local database without resetting progress. Provide a JSON backup through the native share sheet.

Acceptance checks and scope:
Verify finishing an original ten-question lesson, wrong-answer review, a second submission tap, and resuming after force-closing the app. Test alternate accepted spelling, day-boundary streaks, offline launch, denied notifications, large text, and TalkBack/VoiceOver focus. Run native builds and emulator tests for both targets; report any unavailable SDK or device checks explicitly. Exclude copied course material, branded characters, speech scoring, AI tutoring, competitive leagues, subscriptions, and cloud synchronization.

## Originality and assets
The named product is a reference for general workflows only. Use an original product name, visual identity, wording, layout, and assets. Do not copy proprietary code, branded logos, distinctive screens, private APIs, paid templates, or protected media. Use original or appropriately licensed sample data and assets. Build from this brief rather than scraping the reference service. Do not imply affiliation with the referenced company.

## Implementation quality
- Make every visible control work, with clear loading, success, empty, validation, and failure states. Remove controls for unimplemented features.
- Support the target platform and responsive or resizable layouts where appropriate. Use platform-appropriate accessibility semantics, labels, keyboard operation, visible focus, sufficient contrast, and reduced-motion preferences. Provide alternatives for drag-only interactions.
- Validate inputs at the relevant boundary. Treat imported or user-generated content as untrusted; render it safely. Confirm destructive actions or offer undo.
- Keep state changes reliable across navigation and reloads. Never silently lose edits. Handle persistence and network errors with an actionable message.
- Keep the scope realistic. Prioritize the complete primary journey. If a custom Features section differs from the baseline, update the data model, design, and acceptance checks to match it; explicit custom requirements take precedence over baseline assumptions.
- Provide realistic original sample content and a useful empty state. Keep sample data clearly separate from user-created data.

## Delivery and verification
1. Inspect the repository and outline the implementation in a few sentences.
2. Implement the app and connect its actual data flow. Continue until the primary journey works.
3. Run appropriate checks and test the acceptance cases above on the target platform. Verify responsive layouts and keyboard navigation when browser tools are available. For native projects, build with the available SDK and test an emulator or device when possible; report any missing native verification honestly. For games, verify the rules and gameplay loop, not only the menus.
4. Fix observed failures, then provide the runnable result, setup/run instructions, a brief explanation of what is implemented, and any specific configuration or verification limits.

This is a focused MVP. Do not add billing, AI services, or unrelated features unless explicitly requested in the brief. Start building now.