tl;dr

We launched an experimental MDN feature on September 25, 2024 that allows users to choose their preferred language and automatically switch to this language when the requested content is available in that language.

Background

MDN is currently available in English (en-US) and 8 other translated languages (es, fr, ja, ko, pt-BR, ru, zh-CN, zh-TW) and users have always been able to switch to their preferred language manually using the language menu.

Problem

There have been two outstanding issues:

1. Some users prefer English, but their search engine suggests links to their local or native language, so every time these users have to manually switch to their preferred language.
2. Some users prefer a translated language and some content is unavailable in these languages, so MDN links to the English language instead, but this means these users have to manually switch back to their preferred language.

Solution

We have introduced a "Remember language" setting in the language menu. Enabling the setting saves the current language in the preferredlocale cookie, and this will prompt MDN to redirect users whenever they navigate to a page that is available in that language. Disabling the setting will delete the cookie, and users will no longer be redirected.

Note: The cookie has been previously used to save the last language that the user switched to. For this reason, the setting is enabled for all users that have recently switched the language on MDN.

Use case 1: Preference for English

Charlie lives in France and uses French Google, but prefers to read MDN in English, so they enabled "Remember language" while browsing MDN in English.

• Charlie searches for "localstorage" on Google.
• Google suggests https://developer.mozilla.org/fr/docs/Web/API/Window/localStorage in French.
• Charlie clicks on the link.
• Because Charlie's browser sends the preferredlocale=en-US cookie, they now get redirected to English:

  /fr/docs/Web/API/Window/localStorage
  → /en-US/docs/Web/API/Window/localStorage
  

• Charlie no longer has to switch the language manually.

Use case 2: Preference for translated language

Jin lives in South Korea and has basic English knowledge, but prefers to read MDN in Korean, their native language, so they enabled "Remember language" while browsing MDN in Korean.

• Jin is browsing MDN in Korean, and clicks on Blog in the top menu.
• As the Blog is only available in English, Jin is now browsing MDN in English.
• Jin opens the "New JavaScript set methods" blog post.
• The Blog post contains links to several English pages in the MDN Web Docs, like the following one:

  intersection() returns a new set with elements in both this set and the given set.

• Jin clicks on the intersection() link.
• Because Jin's browser sends the preferredlocale=ko cookie and the page is available in Korean, they now get redirected to:

  /en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/intersection
  → /ko/docs/Web/JavaScript/Reference/Global_Objects/Set/intersection
  

• Jin no longer has to switch the language manually.