How to use the @node-red/util.i18n.i function in @node-red/util

get: function(req,res) {
        var namespace = req.params[0];
        var lngs = req.query.lng;
        namespace = namespace.replace(/\.json$/,"");
        var lang = req.query.lng || i18n.defaultLang; //apiUtil.determineLangFromHeaders(req.acceptsLanguages() || []);
        var prevLang = i18n.i.language;
        // Trigger a load from disk of the language if it is not the default
        i18n.i.changeLanguage(lang, function(){
            var catalog = loadResource(lang, namespace);
            res.json(catalog||{});
        });
        i18n.i.changeLanguage(prevLang);
    }
}

get: function(req,res) {
        var namespace = req.params[0];
        var lngs = req.query.lng;
        namespace = namespace.replace(/\.json$/,"");
        var lang = req.query.lng || i18n.defaultLang; //apiUtil.determineLangFromHeaders(req.acceptsLanguages() || []);
        var prevLang = i18n.i.language;
        // Trigger a load from disk of the language if it is not the default
        i18n.i.changeLanguage(lang, function(){
            var catalog = loadResource(lang, namespace);
            res.json(catalog||{});
        });
        i18n.i.changeLanguage(prevLang);
    }
}