Single or multiple translation.json files for i18n?

I'm working a project in Aurelia and using the aurelia-i18n plugin. So far it looks great and translation is working and instantly updating interface language when I change locale.

Question: is there a logical, organizational or performance advantage to using multiple translation files vs. a single translation file? For instance:

Should I just put everything into one file?

my-aurelia/locales/en/translation.json
my-aurelia/locales/es/translation.json

Or should I separate into multiple translation files?

my-aurelia/locales/en/nav.json
my-aurelia/locales/en/words.json
my-aurelia/locales/en/phrases.json

my-aurelia/locales/es/nav.json
my-aurelia/locales/es/words.json
my-aurelia/locales/es/phrases.json

Here's how I have instantiated the plugin for this example (inside the export function configure(aurelia) { of my-aurelia/src/main.js, but I'm at an important design crossroads.

aurelia.use.plugin('aurelia-i18n', (instance) => {
    // register backend plugin
    instance.i18next.use(XHR);

    // adapt options to your needs (see http://i18next.com/docs/options/)
    instance.setup({
      backend: {                                  
        loadPath: '/locales/{{lng}}/{{ns}}.json',
      },
      lng : 'es',
      ns: ['words','phrases','nav'],
      defaultNS: 'words',
      attributes : ['t','i18n'],
      fallbackLng : 'en',
      debug : false
    });
  });

One json language file or multiple json language files? Any additional advice?

Performance-wise, a single file per language will be slightly faster on the initial load because fewer requests are necessary. However, this micro-optimization will be negligible, and you should put more value towards code structure and readability, especially for other people working on the code after you.

Will a single file become so large, that it will be hard for people to find the right entry, and change the content of the JSON file? If not, and you do not expect it to grow to such a size, you're probably best off using a single file.

Will people wonder if you put "Gracias/Thank You" in words (thanks) or phrases (thank you)? I recommend using a structure which is clear for someone who is not familiar with your code.

Lastly, one of the organization structures I have not seen you mention, but which I have used myself, is to order i18n files based on your views. This makes it easy to find the file which needs to be changed, as you already know which view you're working so you don't have to look for the i18n.