Where to store static content (e.g. country codes) in a vue.js app?

You can make any property / function accessible on every vue instance (component) using Vue.prototype.

Vue.prototype.getCountries = {
  'AF': 'Afghanistan',
  'AX': 'Åland Islands',
  'AL': 'Albania',
  'DZ': 'Algeria',
  'AS': 'American Samoa'
};
 
Vue.component('test', {
  template: `<div>{{ getCountries }}</div>`,
  created() {
    console.log('countries ->', this.getCountries);
  }
})
 
new Vue({
  el: '#app',
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.16/vue.min.js"></script>

<div id="app">
  <test />
</div>

Another alternative would be defining a global mixin and will work the same way.

Vue.mixin({
  data() {
    return {
      get getCountries () {
        return {
         'AF': 'Afghanistan',
         'AX': 'Åland Islands',
         'AL': 'Albania',
         'DZ': 'Algeria',
         'AS': 'American Samoa'
      };
    }
  }
})

Personal Preference

I prefer to have it on a .js (notice you also can import mixins to only use it in specific components - Vue Mixins) file and import it only in the components that will be used, to not overload all components with values not required.