use i18n in other function

How to implement multi-language in node.js for template and routers with i18 How can I use i18n in other functions to the language change. i18n only generates empty files en.js es.js ... this is so or is wrong?

Example

//app.js

require(i18n):
require("./router" );

//router.js

export.example = function (){
    .
    .
    .
    req.session.error = __('You have error:  %s', error);
}

500 TypeError: Object # has no method '__'

use the app with i18n internationalization, it is best used only in the final template with this is easier to edit for other languages ​​and not have to search the texts throughout our code.

Use jade for internationalization as follows

#{__('Hello')}

I followed the other information as the reference says.