title: firefox language de-ch (german part of switzerland) not available
body: <p>first of all. i'm aware that i can format numbers using js.
  i would like to avoid to maintain an retrieve a setting from the server which specifies the format</p>
  
  <p>my numbers in question are js floats and should be displayed in the format of the language the user selects in the browser.</p>
  
  <p>i would like to rely on (modern) browser settings to format my decimal numbers
  in switzerland we use the decimal point "."
  so my script gets the navigator.languages[0] value to use it with the <code>intl.date</code> and <code>intl.number</code> - objects (those work fine when feeding in "de-ch" as culture)
  but it turns out on firefox i can only select "de" (Deutsch) as language in the options. This gets used then for the formatting and uses the "," for decimal point.
  why isn't there a "de-ch" (Deutsch-Schweiz) setting in the firefox language options?</p>
  
  <p>my current workaround (and to give a bit more context to this questions) is:</p>
  
  <pre><code>let mostPreferedLanguage = globalThis.navigator.languages[0]
  if (
    mostPreferedLanguage === "de" &amp;&amp;
    navigator.userAgent.toLowerCase().indexOf("firefox") &gt; -1
  ) {
    if ((1.1).toString().indexOf(".") &gt; -1) {
      mostPreferedLanguage = "de-ch"
    }
  }
  export let displayFormats = {
    decimal: {
      default: new Intl.NumberFormat(mostPreferedLanguage, {
        minimumFractionDigits: 2,
        maximumFractionDigits: 2
      }),
      _4Digits: new Intl.NumberFormat(mostPreferedLanguage, {
        minimumFractionDigits: 4,
        maximumFractionDigits: 4
      })
    },
    date: {
      default: new Intl.DateTimeFormat(mostPreferedLanguage, {
        day: "2-digit",
        month: "2-digit",
        year: "numeric"
      }),
      _2DigitsYear: new Intl.DateTimeFormat(mostPreferedLanguage, {
        day: "2-digit",
        month: "2-digit",
        year: "2-digit"
      }),
      defaultTimestamp: new Intl.DateTimeFormat(mostPreferedLanguage, {
        day: "2-digit",
        month: "2-digit",
        year: "2-digit",
        hour: "numeric",
        minute: "numeric",
        second: "numeric",
        hour12: false
      })
    }
  }
  </code></pre>