Why Japanese Sites Show Up in Japanese

When you visit a foreign website, it sometimes automatically displays in your language. Conversely, accessing a Japanese site from abroad might show English. How do websites determine your language?

Your browser sends "I speak Japanese" (or whatever your language is) with every request. Understanding this mechanism explains why you sometimes see the wrong language and how it relates to your privacy.

The Accept-Language Header - Your Browser's Language Card

The most fundamental method websites use to detect language is the Accept-Language header included in every HTTP request.

For example, a browser configured for Japanese sends:

Accept-Language: ja,en-US;q=0.9,en;q=0.8

This means "Japanese is my top priority (q=1.0, the default when omitted), followed by American English (q=0.9), then English in general (q=0.8)." The q value (quality value) ranges from 0 to 1 and indicates language preference priority.

The web server reads this header and selects the highest-priority language it supports. This site uses the same mechanism to switch between Japanese, English, Chinese, and Spanish based on your browser settings.

Geographic Estimation from IP Addresses

When the Accept-Language header is insufficient, websites fall back to GeoIP - estimating geographic location from IP addresses.

If you are accessing from a Japanese IP, the site assumes Japanese. From a German IP, German. However, this approach has limitations:

  • Using a VPN may show the language of the VPN server's country
  • Expatriates see the local language instead of their native one
  • In multilingual countries (Switzerland, Belgium), IP alone cannot determine the language

Most sites therefore prioritize Accept-Language and use GeoIP only as a fallback.

Other Signals Used for Language Detection

  • Cookies / Local Storage: Remember the language a user previously selected. The most reliable method
  • User account settings: Use the language configured in a logged-in user's profile
  • URL path: Include language codes in the URL like /ja/ or /en/. This site uses this approach
  • Browser's navigator.language: The same information as Accept-Language, accessible via JavaScript on the client side

The typical priority order is: explicit user selection > cookie > Accept-Language > GeoIP. A user's deliberate choice is the most trustworthy signal.

Language Settings and Privacy

The Accept-Language header can be used as part of browser fingerprinting.

An unusual language configuration like "Japanese first, then French, then English" can serve as an identifying signal. The priority order, specific quality values, and number of supported languages vary between users, making this header a potential fingerprinting vector.

You can check what language information your browser sends on IP確認さん's homepage, alongside your IP address and browser fingerprint details. It is worth reviewing what data you are transmitting.

To learn more about web internationalization and browser technology, web technology books are an excellent resource.

Related Glossary Terms

HTTP Header Accept-Language is one of the HTTP request headers automatically sent by your browser. Cookie Stores the user's language preference in a cookie for subsequent visits. IP Address GeoIP language estimation is based on IP address geolocation. VPN usage can cause misdetection.