Privacy Policy — Lambda Lingua
Last updated: June 29, 2026
Lambda Lingua (“we”, “our”, or “the app”) is a language learning application developed by an individual developer and available on both Android (Google Play) and iOS (Apple App Store). This policy explains what data is collected, how it is used, and your rights.
1. Data We Collect
1.1 Crash Reports (Firebase Crashlytics)
When the app crashes or encounters an error, we automatically collect:
- Stack trace and error details
- Device model, OS version, and app version
- A random anonymous installation ID (not linked to any personal identity)
This data is used solely to identify and fix bugs.
1.2 Usage Analytics (Firebase Analytics)
We collect anonymous, aggregated usage statistics:
- Which screens are visited and how often
- Which learning language is selected
- General engagement metrics (sessions, retention)
All data is anonymized. We cannot identify you personally from this data.
1.3 Data You Enter
- Flashcard content (words, translations, notes) is stored locally on your device only and is never transmitted to our servers.
- CSV files imported or exported by you remain on your device and are never uploaded anywhere.
- Study session history (which steps you completed, accuracy on quizzes, study streak) is stored locally on your device only.
1.4 In-App Purchases
Subscription purchases are processed entirely by Apple App Store (on iOS) or Google Play (on Android). We do not see or store your payment information, credit card, billing address, or Apple/Google account details. We only receive a confirmation that an active subscription exists for the current user, used to unlock Pro features locally.
1.5 Translation and AI Generation (Server-Side)
When you tap a word for translation or use AI-generated reading/listening content (Pro feature), the app sends the following to our server (a Cloudflare Worker proxy):
- The word, phrase, or short topic prompt
- The source and target language codes
- Your selected CEFR level (for AI generation)
The proxy forwards these requests to DeepL (translation) and DeepSeek (AI text/audio generation). Server-side request logs are retained for 7 days for abuse prevention only and contain no personal identifiers. We do not store or learn from the content of your translation requests.
1.6 App Integrity Verification
To protect our server from abuse and automated misuse, requests to our translation and AI proxy include an attestation token generated by Apple App Attest (on iOS) or Google Play Integrity (on Android). This token confirms that the request comes from a genuine, unmodified copy of the app. It is verified on our server, is not linked to your identity, and contains no personal information such as your name or email.
2. Data We Do NOT Collect
- Name, email address, or any personal identifiers
- Location data
- Contacts or phone data
- Payment information (handled entirely by Apple/Google)
- Advertising identifiers — no IDFA on iOS, no Ad ID on Android; we serve no ads and do not track you across other apps or websites
- Any data from other apps on your device
3. Third-Party Services
| Service | Purpose | Privacy Policy |
|---|---|---|
| Firebase Analytics (Google) | Anonymous usage statistics | policies.google.com/privacy |
| Firebase Crashlytics (Google) | Crash reporting | policies.google.com/privacy |
| ML Kit Translation (Google) | Word translation — processed entirely on-device, no data sent to Google servers | developers.google.com/ml-kit/terms |
| Apple App Store (iOS) | Subscription billing | apple.com/legal/privacy |
| Apple App Attest (iOS) | App-integrity / anti-abuse verification | apple.com/legal/privacy |
| Google Play Billing (Android) | Subscription billing | policies.google.com/privacy |
| Google Play Integrity (Android) | App-integrity / anti-abuse verification | policies.google.com/privacy |
| DeepL (via our proxy) | Server-side translation | deepl.com/privacy |
| DeepSeek (via our proxy) | AI text generation | deepseek.com/privacy-policy |
4. Data Retention
- Crashlytics data is retained for 90 days by Google.
- Analytics data is retained for 14 months (Google Analytics default).
- Cloudflare Worker proxy logs are retained for 7 days, contain no personal identifiers, and are used only for abuse prevention.
- Local app data (your words, progress, session history) stays on your device until you uninstall the app.
5. Children’s Privacy
Lambda Lingua does not knowingly collect data from children under 13. The app contains no advertising and no features that target children specifically.
6. Your Rights
Our analytics and crash reporting are anonymous, tied only to a random installation ID. We serve no ads and collect no advertising identifier (no IDFA on iOS, no Ad ID on Android), so this data is never used for advertising or to track you across other apps or websites.
You can request deletion of any analytics or crash data associated with your anonymous installation ID at any time by contacting us at the email below.
For subscription, refund, or billing concerns — those are handled directly by Apple (iOS) or Google (Android) through your account settings:
- Apple: Settings → [Your Name] → Subscriptions
- Google Play: Play Store → Account → Payments & subscriptions → Subscriptions
7. Changes to This Policy
We may update this policy as new features are added. The “Last updated” date at the top will reflect any changes. Continued use of the app after changes constitutes acceptance.
8. Contact
Questions or requests regarding this privacy policy:
Email: lambdalingua@gmail.com