This is a Feature Proposal

🎩 Description

Documentation related to how to add a new languages needs to be added at the README file.

Related to #1435, #1439

We need to document how to disable or activate any default languages for developing as is explained on those relates issues/PRs.

Related to #1493

In relation with the foundation datepicker localisations, we should add the documentation about how to add languages correctly to those calendars and where to find those locales.

Valid locales can be found on the official repo: https://github.com/najlepsiwebdesigner/foundation-datepicker/tree/master/js/locales
And need to be added on the core folder: decidim/decidim-core/vendor/assets/javascripts/datepicker-locales

Also It's a must to add the respective formating locales at decidim-admin/config/locales/xx.yml as the following example:

time:
    formats:
      datepicker: "%m/%d/%Y"
      timepicker: "%d/%m/%Y %H:%M"