app/javascript/controllers/datepicker_loader.js
import flatpickr from 'flatpickr'
import { Japanese } from 'flatpickr/dist/l10n/ja'
const localeDict = {
en: null,
ja: Japanese
}
window.addEventListener('turbo:load', () => {
const locale = document.getElementsByTagName('body')[0].getAttribute('data-locale')
flatpickr('.date-picker', {
allowInput: true,
locale: localeDict[locale]
})
})