JavaScript for detecting browser language preference [duplicate]

Answer 1

I've been using Hamid's answer for a while, but it in cases where the languages array is like ["en", "en-GB", "en-US", "fr-FR", "fr", "en-ZA"] it will return "en", when "en-GB" would be a better match.

My update (below) will return the first long format code e.g. "en-GB", otherwise it will return the first short code e.g. "en", otherwise it will return null.

function getFirstBrowserLanguage() {
        var nav = window.navigator,
            browserLanguagePropertyKeys = ['language', 'browserLanguage', 'systemLanguage', 'userLanguage'],
            i,
            language,
            len,
            shortLanguage = null;

        // support for HTML 5.1 "navigator.languages"
        if (Array.isArray(nav.languages)) {
            for (i = 0; i < nav.languages.length; i++) {
                language = nav.languages[i];
                len = language.length;
                if (!shortLanguage && len) {
                    shortLanguage = language;
                }
                if (language && len>2) {
                    return language;
                }
            }
        }

        // support for other well known properties in browsers
        for (i = 0; i < browserLanguagePropertyKeys.length; i++) {
            language = nav[browserLanguagePropertyKeys[i]];
            //skip this loop iteration if property is null/undefined.  IE11 fix.
            if (language == null) { continue; } 
            len = language.length;
            if (!shortLanguage && len) {
                shortLanguage = language;
            }
            if (language && len > 2) {
                return language;
            }
        }

        return shortLanguage;
    }

console.log(getFirstBrowserLanguage());

Update: IE11 was erroring when some properties were undefined. Added a check to skip those properties.