Detecting Browser Language Preference with JavaScript

When developing web applications, it is often necessary to detect the language preference of the user's browser to provide localized content and enhance user experience. JavaScript provides several properties to access language information, but the specific properties that return the desired values may vary depending on the browser and operating system being used.

In Internet Explorer, the preferred language can be set in Tools > Internet Options > General > Languages. However, JavaScript's navigator.language property may not always accurately reflect this setting. To detect the language preference in IE, one can use the navigator.userLanguage property, which retrieves the setting configured in Start > Control Panel > Regional and Language Options > Regional Options.

In Firefox, the language preference can be found in Tools > Options > Content > Languages. However, navigator.language may not reliably provide this information. Instead, using navigator.browserLanguage or navigator.systemLanguage is recommended.

Unfortunately, there is no direct method in JavaScript to access the HTTP 'Accept-Language' header, which is affected by the browser language preferences. However, a workaround can be implemented by using a third-party endpoint or a proxy to retrieve the header value. For example, a Google App Engine script can be utilized to return the request headers via JSONP, allowing you to obtain the 'Accept-Language' header from within JavaScript.