index.js

const Koa = require('koa');
const i18next = require('i18next');
const app = new Koa();
import LD from "koa-i18next-detector";

const i18m = require('./src');

i18next.use(LD).init({
    fallbackLng: 'en',
    preload: ['en', 'es'],
    resources: {
        en: {
            translation: {
                "key": "hello world"
            }
        },
        es: {
            translation: {
                "key": "es hello world es"
            }
        }
    },
    detection: {
        order: ['querystring', /*'path', 'cookie',*/ 'header', 'session'],

        lookupQuerystring: 'lng',

        lookupParam: 'lng', // for route like: 'path1/:lng/result'
        lookupFromPathIndex: 0,

        lookupCookie: 'i18next',
        // cookieExpirationDate: new Date(), // default: +1 year
        // cookieDomain: '', // default: current domain.

        lookupSession: 'lng',

        // cache user language
        caches: false // ['cookie']
    }
}, (err, t) =>{
    // initialized and ready to go!
    const hw = i18next.t('key'); // hw = 'hello world'
    console.log(hw);
});

app.use(i18m.getHandler(i18next, {
        locals: 'locals',
        ignoreRoutes: ['/no-lng-route'],
    })
);

// response
app.use(async (ctx, next) =>{
    await next();
    if (ctx.request.lng) {
        ctx.body = ctx.response.locals.t(`key`);
    } else {
        ctx.body = 'No language detected!'
    }
});

app.listen(3000, function(){
    console.log('server listening');
});