Topic on Project:Support desk

Hello,

I'm tring to create a script that changes the MediaWiki interface language via javascript based on the page language at my private wiki.

For logged-in users I'm able to do that by changing the user's options via an API request as shown below, but this do not work for anonymous users. So my question is: Is it possible to change the interface language for anonymous users/visitors via JavaScript? And how do I do that?

/**
 * Automatic switch of wgUserLanguage, based on wgPageContentLanguage
 * The output of Template:AutoLangSwitch (id='auto-lang-switch') is the triger
**/
( function ( $, mw ) {
	mw.loader.using( 'mw.Api' ).then( function () {
		var nsNumber = mw.config.get( 'wgNamespaceNumber' );
		var lgAction = mw.config.get( 'wgAction' );
		var pageLang = mw.config.get( 'wgPageContentLanguage' );
		var userLang = mw.config.get( 'wgUserLanguage' );
		var langTest = document.getElementById( 'auto-lang-switch' );
		
		if ( pageLang !== userLang && lgAction === 'view' && nsNumber === 0 && langTest ) {
			var params = {
				action: 'options',
				change: 'language=' + pageLang,
				format: 'json'
			},
			api = new mw.Api();
			api.postWithToken( 'csrf', params ).done( function ( data ) {
				console.log( data );
			} );
			location.reload();
		}
	} );
}( jQuery, mediaWiki ) );

The best way to do this, is to use MediaWiki:Gadget-AnonymousI18N.js from commons and install that as a hidden gadget.

https://commons.wikimedia.org/wiki/MediaWiki:Gadgets-definition

https://commons.wikimedia.org/wiki/MediaWiki:Gadget-AnonymousI18N.js

Hi, @TheDJ, thank you for the replay and the shared script! I was thinking about the possibility to use the parameter ?uselang=xx (like it is made in Gadget-AnonymousI18N.js), but I found this solution too complicated.

Finally I found a simple way how to engage Extension:UniversalLanguageSelector for this task. ULS writes two cookies: _language=xx and _mwuser-sessionId=xxyyzz. All we need in order to solve the current task is to set the language cookie and reload the page. So, for anonymous users the script could be:

/**
 * Automatic switch of wgUserLanguage, based on wgPageContentLanguage 
 * by the help of Extension:ULS
 * The output of Template:AutoLangSwitch (id='auto-lang-switch') is the triger
**/
( function ( $, mw ) {
	var nsNumber = mw.config.get( 'wgNamespaceNumber' );
	var lgAction = mw.config.get( 'wgAction' );
	var pageLang = mw.config.get( 'wgPageContentLanguage' );
	var userLang = mw.config.get( 'wgUserLanguage' );
	var langTest = document.getElementById( 'auto-lang-switch' );
	
	if ( pageLang !== userLang && lgAction === 'view' && nsNumber === 0 && langTest ) {
		mw.cookie.set('language', pageLang);
		location.reload();
	}
}( jQuery, mediaWiki ) );

According to that the final script that works for logged-in and anonymous users is:

/**
 * Automatic switch of wgUserLanguage, based on wgPageContentLanguage 
 * by the help of Extension:ULS and mw.Api
 * The output of Template:AutoLangSwitch (id='auto-lang-switch') is the triger
 */
( function ( $, mw ) {
	var userId    = mw.config.get( 'wgUserId' );
	var nsNumber  = mw.config.get( 'wgNamespaceNumber' );
	var lgAction  = mw.config.get( 'wgAction' );
	var pageLang  = mw.config.get( 'wgPageContentLanguage' );
	var userLang  = mw.config.get( 'wgUserLanguage' );
	var cookLang  = mw.cookie.get('language');
	var allowedNS = [0, 1, 4, 5, 14, 15];
	var langTest  = document.getElementById( 'auto-lang-switch' );

	// Logged-in users
	if ( pageLang !== userLang && lgAction === 'view' && userId !== null && allowedNS.includes(nsNumber) && langTest ) {
		mw.loader.using( 'mw.Api' ).then( function () {
			var params = {
				action: 'options',
				change: 'language=' + pageLang,
				format: 'json'
			},
			api = new mw.Api();
			api.postWithToken( 'csrf', params ).done( function ( data ) {
				console.log( data );
			} );
			location.reload();
		} );
	} else // Anonymous users
	if ( pageLang !== userLang && lgAction === 'view' && userId === null && cookLang !== pageLang && allowedNS.includes(nsNumber) && langTest ) {
		var sessionId = mw.cookie.get( 'mwuser-sessionId');
		if ( sessionId ) {
			console.log('mwuser-sessionId: ' + sessionId);
		} else {
			sessionId = mw.user.generateRandomSessionId();
			mw.cookie.set( 'mwuser-sessionId', sessionId, { expires: null } );
		}
		
		mw.cookie.set('language', pageLang); 
		location.reload();
	}
}( jQuery, mediaWiki ) );

Just make sure you vary cache on the cookie header for anonymous users in that case, otherwise people might get unexpected results from proxies.

Thank you for the help, @TheDJ. I've added mw.cookie.set( 'mwuser-sessionId', sessionId) in the script above.