Change locale i18n Node.js

I can't find how to change locale in i18n

https://github.com/mashpie/i18n-node

I configure like that

i18n.configure({
    // setup some locales - other locales default to en silently
    locales:['en', 'de'],

    // where to register __() and __n() to, might be "global" if you know what you are doing
    register: global
});

But I always have en as locale, I can't find how to set de

Thanks