I want native country and language selects in HTML

ISO 3166 (for countries) and ISO 639 (for languages) are widely used international standards in information exchange. Websites routinely ask users to select a country or language, but every author must supply and maintain the full list of acceptable values individually. Although projects like Unicode CLDR provide translations and locale-appropriate sort orders for these items, authors must include all of that data themselves.

I want <select> (or perhaps <input>) elements to have a special mode for selecting a country or a language, triggered by an attribute value, so browsers can provide a built-in, localised picker backed by ISO 3166 and ISO 639.

Authors would also need to be able to specify valid values either explicitly or implicitly — by declaring only additions and exclusions from the default set — without having to supply more than the standard two- or three-letter codes. This could work similarly to <input list="…"> with <datalist>:

<datalist id="excluded-countries">
  <option value="ru"></option>
</datalist>
<datalist id="additional-countries">
  <option value="eu"></option>
</datalist>

<datalist id="supported-languages">
  <option value="en"></option>
  <option value="en-US"></option>
  <option value="es"></option>
  <option value="pt-BR"></option>
</datalist>