[gatsby-theme-i18n] Help me to teach him good behavior ;)

[JOduMonT]

I must admit, I'm not a new age programmer (node, python...) and my notion are rusty.
I believe I followed with success the steps to install gatsby-theme-i18n on top of Gatsby Starter Blog

gatsby-config.js

...
    {
      resolve: `gatsby-theme-i18n`,
      options: {
        defaultLang: `en`,
/*        prefixDefault: `true`, /* ref: https://github.com/gatsbyjs/themes/discussions/114 */
        configPath: require.resolve(`./i18n/config.json`),
      },
    },
...

i18n/config.json

[
    {
      "code": "en",
      "hrefLang": "en-CA",
      "name": "English",
      "localName": "English",
      "langDir": "ltr",
      "dateFormat": "YYYY-MM-DD"
    },
    {
      "code": "fr",
      "hrefLang": "fr-CA",
      "name": "French",
      "localName": "Français",
      "langDir": "ltr",
      "dateFormat": "YYYY-MM-DD"
    }
   ]

But then
when I visit the http://127.0.0.1:8000/fr/hello-world which is ./content/blog/hello-world/index.fr.md to see the post properly the url have to be: http://127.0.0.1:8000/fr/hello-world/index.fr/ unless I have a

• http://127.0.0.1:8000/fr/hello-world/ = the post in english even if in the url point to /fr/
• from the blog list http://127.0.0.1:8000/fr/ if I click on the title is bring me to: http://127.0.0.1:8000/hello-world/index.fr/ which end on a 404 error

So, what am I missing?