Privacy Policy

Dual Subtitles browser extension · Last updated: July 29, 2026

This Privacy Policy explains what data the Dual Subtitles browser extension (“the extension”, “we”) handles and why. We keep the extension’s data use as narrow as possible: everything described below exists only to show subtitles and translate words.

Data we do not collect

• We do not ask for your name, email address, or any other personal details.
• We do not create user accounts with credentials, and we do not use passwords.
• We do not collect your browsing history, and we do not track which pages you visit outside of the video pages the extension supports.
• We do not sell, rent, or share your data with third parties for advertising or any other unrelated purpose.
• We do not upload your local video files. When you open a video file from your computer, the file is played and processed entirely inside your browser and never leaves your device.

Data stored on your device

The following is kept locally in your browser’s extension storage and is not sent to us:

• Your settings: languages, subtitle appearance, playback preferences.
• Your personal word list: words you marked as known, being learned, or ignored, together with their translations.
• A temporary cache of subtitles and dictionary lookups, so the same video does not have to be fetched twice.
• Which subtitles you bound to a particular video file, so the extension can restore them the next time you open it.

You can erase all of this at any time by removing the extension from your browser.

Data sent to our server

To find and prepare subtitles, the extension contacts our server at api.lingflix.app and may send:

• the identifier of the video you are watching on a supported site;
• the language codes you selected;
• for local video files: a checksum of the file and, if you use the search, the title you typed. The video itself is never sent;
• subtitle text, when it has to be translated or synchronized on the server.

The extension signs in to our server anonymously in the background. This creates a random identifier that lets the server apply usage limits and prevent abuse. It is not linked to your identity, your Google account, or any personal information.

Third-party services

The extension sends requests to the following services only when the corresponding feature is used:

• Google Translate — the word or phrase you clicked, together with the source and target language, in order to translate it and to pronounce it aloud.
• Google Firebase Authentication — to create and refresh the anonymous identifier described above.
• OpenSubtitles — to download public subtitle files for local video files.
• YouTube and Netflix — to read the subtitle tracks of the video you are currently watching, in the same way the player itself does.

These services process the requests under their own privacy policies. We do not send them anything beyond what is listed above.

Permissions

The browser will ask you to grant the extension a number of permissions. Each one is required for a specific feature: storing your settings and word list, displaying subtitles on supported video sites, reading the subtitle tracks the video player requests, and downloading subtitle files. The extension does not use these permissions for anything else.

Children

The extension is not directed at children under 13, and we do not knowingly collect any information from them.

Changes to this policy

If the way the extension handles data changes, this page will be updated and the date at the top of the page will change accordingly.

Contact us

If you have any questions about this Privacy Policy, write to support@dualsubtitles.app.