Last updated: September 14, 2026

Privacy Policy

The Short Version

I built SifuLingo to help people learn languages, not to harvest data. I collect only what's necessary to make the app work, I don't sell your information to anyone, and I'm transparent about what happens with your data.

If you have questions about anything here, just reach out. I'm a solo developer, so you'll be talking directly to the person who built this.

Who We Are

SifuLingo is operated as a solo project. The service is available at sifulingo.de. For any privacy-related questions or requests, you can contact me at [email protected].

Note: I'm currently operating as a freelancer/solopreneur. A formal business address will be added here once the company is officially registered.

What Data We Collect

I collect only what's necessary to make SifuLingo work:

  • Account Information: Your name and email address when you sign up. That's it for personal data.
  • Learning Preferences: Your native language, target language, and proficiency level - so we can personalize your learning experience.
  • Your Learning Content: The flashcards you create, words you add, your review history, and learning progress. This is your vocabulary data that makes the spaced repetition system work.
  • Technical Data: Basic session information (IP address, browser type) to keep your account secure and the app functional.
  • Images for OCR: When you scan text with your camera, those images are sent to AI services for text extraction. Important: we don't store these images - they're processed and immediately discarded.

What We Don't Collect

Just as important - here's what I deliberately don't collect:

  • No third-party tracking pixels or analytics scripts - I don't track your behavior across the web
  • No Google Analytics or similar tools - I'm not interested in detailed behavioral analytics
  • No unnecessary cookies - only functional session cookies, plus one anonymous visit counter that's gone when you close your browser
  • No social media tracking or sharing buttons that leak your data

How We Use Your Data

Your data is used for exactly what you'd expect:

  • To provide the core service - managing your flashcards, scheduling reviews, tracking progress
  • To generate personalized content - AI-powered vocabulary suggestions and practice stories tailored to your level
  • To send you transactional emails - welcome messages, password resets, important updates about the service
  • To process payments securely through Paddle (more on that below)
  • To improve the service - but only using aggregated, anonymized data (e.g., "users review an average of X cards per session")

Future consideration: I may use anonymized, non-personal learning data (like flashcard content or story topics) to improve AI recommendations. If this happens, I'll update this policy and notify users. I will never use your personal information (name, email, etc.) for training purposes.

Third-Party Services

I use a few carefully selected services to make SifuLingo work. Here's the complete list and what they do:

Paddle (Payment Processing)

Paddle handles all payment processing. When you subscribe, Paddle collects your payment information directly - I never see or store your credit card details. Paddle is the "merchant of record," which means they handle billing, VAT compliance, and customer payment data. Check out Paddle's privacy policy for details on how they handle your payment data.

OpenAI & Google Gemini (AI Processing)

When you use AI features (vocabulary suggestions, story generation, or text extraction from images), your content is sent to OpenAI or Google Gemini for processing. This includes:

  • Text you scan with your camera (for OCR extraction)
  • Your learning preferences and level (to generate appropriate content)
  • Words you've added (to create personalized vocabulary suggestions)

These services process your content to provide the AI features, but according to their policies, they don't use customer data to train their models. See OpenAI's privacy policy and Google's privacy policy.

Resend (Email Delivery)

Transactional emails (welcome messages, password resets, notifications) are sent via Resend. They only handle email delivery and don't use your data for any other purpose. See Resend's privacy policy.

Hosting

The app, its database, file storage and backups all live on servers in Europe. The hosting providers run the machines but don't access your data.

Cookies

SifuLingo uses minimal cookies - only what's essential:

  • Session Cookie: Keeps you logged in and maintains your session. This is essential for the app to function.
  • Visit Counter (sl_vid): A random id so I can count visits without counting your page views twice. It holds nothing about you and is deleted when you close your browser.
  • First Visit Source (sl_attribution): The site or campaign link that first brought you here, so I can see which links lead to signups. No id, nothing about you, and deleted when you close your browser.
  • Paddle Cookies: If you subscribe, Paddle may set cookies to manage the checkout process. See Paddle's cookie policy.

No advertising cookies, and nothing that follows you across other sites. Your browser settings can control cookies, but blocking the session cookie will prevent you from staying logged in.

Data Security

I take reasonable measures to protect your data:

  • All data transmission uses HTTPS encryption
  • Passwords are hashed using industry-standard bcrypt
  • Infrastructure is hosted on secure servers in Europe with regular updates
  • Access to the database is restricted and monitored

That said, no system is 100% secure. I do my best, but if a security breach occurs, I'll notify affected users promptly and transparently.

Your Rights (GDPR)

Under EU law (GDPR), you have these rights:

  • Access: Request a copy of all data I have about you
  • Correction: Update your account information anytime in settings
  • Deletion: Delete your account and all associated data immediately
  • Export: Download your flashcards and learning data (feature coming soon)
  • Objection: Opt out of data processing for certain purposes (though this may limit functionality)

To exercise these rights, email me at [email protected]. I'll respond within 30 days.

Data Retention & Deletion

Your data stays around only as long as you need it:

  • Active accounts: Your data is kept as long as your account is active
  • Account deletion: When you delete your account, all your data (flashcards, learning history, preferences) is permanently deleted immediately
  • Payment records: Financial transaction records may be retained by Paddle for tax and legal compliance (typically 7 years) - this is outside my control

Age Requirements

You must be at least 16 years old to use SifuLingo. This complies with GDPR requirements for processing data of minors without parental consent. If you're under 16, please have a parent or guardian create an account for you.

International Transfers

Your data is primarily stored in Europe. However, when using AI features, your content is sent to OpenAI (US-based) and Google (with servers worldwide). These companies have mechanisms in place for legal data transfers, but be aware your data may cross borders.

If you're uncomfortable with this, you might want to avoid using the AI-powered features - though that would significantly limit the app's functionality.

Changes to This Policy

I may update this privacy policy occasionally to reflect changes in the service or legal requirements. When I do:

  • The "Last updated" date at the top will change
  • For significant changes, I'll notify you by email
  • Continued use of SifuLingo after changes means you accept the updated policy

Questions?

If anything here is unclear or you have concerns about your privacy, reach out at [email protected]. I'm a solo developer, so you'll get a response from the actual person who built this - no customer service scripts.