Detects the primary language of the content in a tab, using the Compact Language Detector (CLD).

This is an asynchronous function that returns a Promise.


var detecting = browser.tabs.detectLanguage(
  tabId,                  // optional integer
  callback                // optional function


tabId Optional
integer. Defaults to the active tab of the current window.
callback Optional
function. Currently, if a tabId is specified, this method uses this callback to return the results instead of returning a promise. The callback receives as its only input parameter a string containing the detected language code such as en or fr.

Return value

A Promise that will be fulfilled with a string representing an ISO language code such as en or fr. For a complete list of languages supported by this method, see kLanguageInfoTable. For an unknown language, "und" will be returned (but see bug 1288263). If any error occurs the promise will be rejected with an error message.


Detect and log the language of the active tab when the user clicks a browser action:

function onLanguageDetected(lang) {
  console.log(`Language is: ${lang}`);

function onError(error) {
  console.log(`Error: ${error}`);

browser.browserAction.onClicked.addListener(function() {
  var detecting = browser.tabs.detectLanguage();
  detecting.then(onLanguageDetected, onError);

Detect and log the language of every open tab when the user clicks a browser action (note that this example requires the "tabs" permission):

function onLanguageDetected(url, lang) {
  console.log(`Language in ${url} is: ${lang}`);

function onError(error) {
  console.log(`Error: ${error}`);

function detectLanguages(tabs) {
  for (tab of tabs) {
    var onFulfilled = onLanguageDetected.bind(null, tab.url);
    var detecting = browser.tabs.detectLanguage(;
    detecting.then(onFulfilled, onError);

browser.browserAction.onClicked.addListener(function() {
  var querying = browser.tabs.query({});
  querying.then(detectLanguages, onError);

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxOperaFirefox for Android
detectLanguageChrome Full support YesEdge Full support 14Firefox Full support 45Opera Full support YesFirefox Android No support No


Full support  
Full support
No support  
No support

This API is based on Chromium's chrome.tabs API. This documentation is derived from tabs.json in the Chromium code.

Microsoft Edge compatibility data is supplied by Microsoft Corporation and is included here under the Creative Commons Attribution 3.0 United States License.

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