Return `Not Found` in koa-router

Question

In app.js, I have some code like following

 const Router = require('koa-router')
 let enpackage = new Router()
 enpackage.get('/en', async ( ctx )=>{
   ctx.redirect('/')
 })
 let router = new Router()
 router.use('/en', enpackage.routes(), enpackage.allowedMethods())
 app.use(router.routes()).use(router.allowedMethods())

And I try to visit localhost:3000/en, it will return error Not Found, please help me.