Access i18next Translation in Function not in App.js

Im using ExpressJS and i18next.

in app.js

var express = require('express')
  , i18n = require('i18next')
  , user = require('./routes/user')
...
//internationalization
i18n.init({
  lng: 'en-US',
  saveMissing: true,
  debug: true
});
...  
app.use(i18n.handle);
app.set('views', __dirname + '/views');
app.set('view engine', 'jade');
...
i18n.registerAppHelper(app);
...
app.post('/users/save', user.save);

I can access the translation in jade:

t('app.title')

How can I access the translation in routes.user.js

exports.save = function(req, res){
    //t('app.title')
}