Yahoo! UI Library

/**
 * The Intl utility provides a central location for managing sets of
 * localized resources (strings and formatting patterns).
 *
 * @class Intl
 * @uses EventTarget
 * @static
 */

var SPLIT_REGEX = /[, ]/;

Y.mix(Y.namespace('Intl'), {

 /**
    * Returns the language among those available that
    * best matches the preferred language list, using the Lookup
    * algorithm of BCP 47.
    * If none of the available languages meets the user's preferences,
    * then "" is returned.
    * Extended language ranges are not supported.
    *
    * @method lookupBestLang
    * @param {String[] | String} preferredLanguages The list of preferred
    * languages in descending preference order, represented as BCP 47
    * language tags. A string array or a comma-separated list.
    * @param {String[]} availableLanguages The list of languages
    * that the application supports, represented as BCP 47 language
    * tags.
    *
    * @return {String} The available language that best matches the
    * preferred language list, or "".
    * @since 3.1.0
    */
    lookupBestLang: function(preferredLanguages, availableLanguages) {

        var i, language, result, index;

        // check whether the list of available languages contains language;
        // if so return it
        function scan(language) {
            var i;
            for (i = 0; i < availableLanguages.length; i += 1) {
                if (language.toLowerCase() ===
                            availableLanguages[i].toLowerCase()) {
                    return availableLanguages[i];
                }
            }
        }

        if (Y.Lang.isString(preferredLanguages)) {
            preferredLanguages = preferredLanguages.split(SPLIT_REGEX);
        }

        for (i = 0; i < preferredLanguages.length; i += 1) {
            language = preferredLanguages[i];
            if (!language || language === '*') {
                continue;
            }
            // check the fallback sequence for one language
            while (language.length > 0) {
                result = scan(language);
                if (result) {
                    return result;
                } else {
                    index = language.lastIndexOf('-');
                    if (index >= 0) {
                        language = language.substring(0, index);
                        // one-character subtags get cut along with the
                        // following subtag
                        if (index >= 2 && language.charAt(index - 2) === '-') {
                            language = language.substring(0, index - 2);
                        }
                    } else {
                        // nothing available for this language
                        break;
                    }
                }
            }
        }

        return '';
    }
});