Privacy Policy

Last updated: October 10, 2026

Viktor Ralchenko ("we", "us", or "our") operates the Deutsch Lernen mobile application (the "App"). This Privacy Policy explains how we collect, use, and protect your information when you use our App.

1. Information We Collect

1.1 Data Stored Locally on Your Device

The App stores the following data locally on your device only:

• Learning progress — vocabulary review history, flashcard ratings, grammar exercise scores, streaks, and study time
• User preferences — selected CEFR level, daily goal, TTS speed, dark mode setting, and interface language
• Chat history — conversations with the AI tutor

This data remains on your device. Uninstalling the App will delete all locally stored data. The only data that leaves your device is described in section 1.2.

1.2 Data Sent Off Your Device

• AI features (Chat, Speaking, Writing) without your own API key: your messages, the selected CEFR level and an anonymous installation ID are sent over HTTPS to our server (a Cloudflare Worker), which forwards the messages to the Google Gemini API and returns the reply. The installation ID is a random number generated by the App; it is not linked to your name, account or device hardware and is used only to count how many AI messages you have used. Our server stores only that message count — never the content of your messages. We use Google's free Gemini API tier, under which Google may use the content of requests to improve its products. Please do not enter personal or sensitive information in AI conversations.
• Subscription check: if you have a Premium subscription, its Google Play purchase token is sent to our server so it can verify the subscription with Google Play. If you redeemed a promo code, the code is sent instead.
• AI features with your own API key: if you enter your own key for Groq, Google Gemini, OpenAI or Anthropic Claude in Settings, your messages and CEFR level are sent directly to that provider and do not pass through our server. That provider's privacy policy applies. Your key is stored only on your device.
• Advertising: free users see ads served by Google AdMob, which may collect your device's advertising ID and usage data to show and measure ads. Premium users do not see ads.
• Payments: Premium subscriptions are processed entirely by Google Play. We never see your payment information.

1.3 Data We Do NOT Collect

We do not collect:

• Personal information (name, email, address, phone number)
• Location data
• Contacts, photos, or files
• Payment or financial information

We do not use analytics or tracking services of our own.

2. How We Use Information

All learning data is used solely to:

• Track your study progress and streaks
• Schedule flashcard reviews using the FSRS spaced repetition algorithm
• Adapt AI tutor responses to your CEFR level
• Display statistics and weak areas

3. Third-Party Services

The App uses the following third-party services:

• Google Gemini API — AI replies when you do not use your own key. See Gemini API Terms and Google's Privacy Policy.
• Cloudflare Workers — hosts our server that forwards AI requests and counts usage. See Cloudflare's Privacy Policy.
• Groq, OpenAI, Anthropic, Google Gemini — only if you enter your own API key for them. See Groq, OpenAI, Anthropic.
• Google AdMob — ads for free users. See how Google uses data in ads.
• Google Play Billing — for subscription management. See Google's Privacy Policy.
• Android Text-to-Speech and Speech Recognition — built-in system services for pronunciation and speaking practice, provided by your device.

4. Data Security

Learning data is stored locally on your device using Android's standard storage mechanisms. All network communication (our server, AI providers, Google Play) uses HTTPS encryption. Our server keeps only per-installation AI message counts and short-lived subscription check results; it does not store message content.

5. Children's Privacy

The App is not directed at children under 13. We do not knowingly collect personal information from children under 13. If you are a parent or guardian and believe your child has provided personal information, please contact us.

6. Data Deletion

Learning data is stored locally on your device, and you can delete it at any time by:

• Uninstalling the App, or
• Clearing the App's data in Android Settings > Apps > Deutsch Lernen > Storage > Clear Data

Doing either also discards the anonymous installation ID. The message count linked to it on our server cannot be connected to you; to have it deleted anyway, email us.

7. Subscriptions

The App offers optional Premium subscriptions (monthly and yearly) through Google Play. Subscription management, billing, and cancellation are handled by Google Play. You can manage your subscription in Google Play Store > Subscriptions.

8. Changes to This Policy

We may update this Privacy Policy from time to time. Changes will be reflected in the "Last updated" date above. Continued use of the App after changes constitutes acceptance of the updated policy.

9. Contact Us

If you have questions about this Privacy Policy, contact us at:

Email: vralchenko@gmail.com

Developer: Viktor Ralchenko