Build Angular Translate with Grunt

Question

I'm using Yeoman to build an Angular app, with Grunt.

I'm using Angular Translate, and got a problem when I build the app with Grunt with the module Grunt Angular Translate.

I have 2 languages, french and english (fr.json & en.json), in a app/translations folder.

I have this config in my Gruntfile.js:

i18nextract: {
  default_options: {
    src: ['app/**/*.js', 'app/**/*.html', 'app/**/*.json'],
    suffix: '.json',
    lang: ['fr', 'en'],
    dest: 'dist/translations',
    jsonSrc: ['app/translations/*.json']
  }
}

This create 2 files, fr.json & en.json in dist/translations, each contains all translations key, but not the corresponding values:

For example:

"email-in": "",
"email-out": "",
"call-in": "",
"call-out": "",

I tried many configurations but couldn't find the right one to solve this.

Thanks for your help.