shopify-custom-i18n.js

window.i18n = window.i18n || {};

i18n._langCache = {}

i18n._availableLangs = [
  'en',
  'zh-TW',
  'ja'
]

i18n._updateElements = function () {
  let elements = document.querySelectorAll('*')
  elements.forEach(function (element) {
    let langIndex = element.getAttribute('data-lang-content')
    let langPack = i18n._langCache[i18n._lang]
    if (langIndex) {
      let langTarget = langPack
      langIndex.split('.').forEach(function (layer) {
        langTarget = langTarget[layer]
      })
      element.innerHTML = langTarget
    }
  })
}

i18n.changeLanguage = function (lang) {
  this._lang = lang
  $.cookie('shopify.custom-lang', lang)

  if (!i18n._langCache.hasOwnProperty(lang)) {
    let langPackUrl = '{{ "locales..json" | asset_url }}'.replace('s..j', 's.' + lang + '.j')

    $.ajax({
      url: langPackUrl,
      type: 'GET',
      dataType: 'json',
      async: false
    }).success(function (langPack) {
      i18n._langCache[lang] = langPack
      i18n._updateElements()
    }).fail(function (error) {
      console.error('error', error)
    })
  } else {
    i18n._updateElements()
  }
}

$("#changeLanguageDropdown a").click(function (event) {
  let lang = event.target.getAttribute('data-lang')
  i18n.changeLanguage(lang)
})

i18n.autoDetectLanguage = function () {
  if ($.cookie && $.cookie('shopify.custom-lang')) {
    let lang = $.cookie('shopify.custom-lang')
    i18n.changeLanguage(lang)
  } else {
    $.ajax({
      url: '//ajaxhttpheaders.appspot.com',
      type: 'POST',
      asunc: false,
      dataType: 'jsonp',
      success: function (headers) {
        let preferredLangs = headers['Accept-Language'].split(';')[0].split(',')
        var lang = 'en'
        preferredLangs.some(function (preferredLang) {
          if (i18n._availableLangs.includes(preferredLang)) {
            lang = preferredLang
            return true
          }
        })
        i18n.changeLanguage(lang)
      }
    })
  }
}
i18n.autoDetectLanguage()

Thanks @Asoul !!!

I keep getting this errors:

But can't figure out what I'm missing. Any ideas?

Thank you! @Asoul