These docs are for an old release. Info on upgrading to v6
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locale

The locale and locales options allow you to localize certain aspects of the calendar:

Loading Locales for an ES6 build system

If you are using an ES6 build system and want to load a specific locale, do something like this:

import { Calendar } from '@fullcalendar/core';
import esLocale from '@fullcalendar/core/locales/es';
...
let calendar = new Calendar(calendarEl, {
  locale: esLocale
});
...

If you want to load multiple specific locales with the ability to switch between them after pageload, do something like this:

import { Calendar } from '@fullcalendar/core';
import esLocale from '@fullcalendar/core/locales/es';
import frLocale from '@fullcalendar/core/locales/fr';
...
let calendar = new Calendar(calendarEl, {
  locales: [ esLocale, frLocale ],
  locale: 'fr' // the initial locale. if not specified, uses the first one
});
...
calendar.setOption('locale', 'es');

If you want to load ALL locales have the ability to switch between them after pageload, do something like this:

import { Calendar } from '@fullcalendar/core';
import allLocales from '@fullcalendar/core/locales-all';
...
let calendar = new Calendar(calendarEl, {
  locales: allLocales,
  locale: 'fr' // the initial locale
});
...
calendar.setOption('locale', 'pt-br');

Loading Locales with Script Tags and Browser Globals

If you are using script tags and browser globals and want to load a specific locale, do something like this:

<script src='fullcalendar/core/main.js'></script>
<script src='fullcalendar/core/locales/es.js'></script>
<script>
...
var calendar = new FullCalendar.Calendar(calendarEl, {
  locale: 'es'
});
...
</script>

If you want to load ALL locales have the ability to switch between them after pageload, do something like this:

<script src='fullcalendar/core/main.js'></script>
<script src='fullcalendar/core/locales-all.js'></script>
<script>
...
var calendar = new FullCalendar.Calendar(calendarEl, {
  locale: 'es'
});
...
calendar.setOption('locale', 'fr');
</script>

For more information, view a live demo.