wpadverts

The new currency you can add using this code snippet https://github.com/simpliko/wpadverts-snippets/blob/master/add-currency/add-currency.php

As for having multiple currencies on-site i am afraid we do not have such feature in WPAdverts, it is only possible to have one currency. The only possible workaround is to disable currency validation so the users will be able to enter any text in the price field.

You can do that by adding the code below in your theme functions.php file

add_filter( "adverts_form_load", "disable_currency_validation_form_load" );
function disable_currency_validation_form_load( $form ) {
  if( $form['name'] != "advert" ) {
    return $form;
  }
  foreach( $form["field"] as $key => $field ) {
    if( $field["name"] == "adverts_price" ) {
        $form["field"][$key]["class"] = "";
        $form["field"][$key]["filter"] = array();
    }
  }
  return $form;
}
add_filter( "adverts_get_the_price", "disable_currency_validation_get_price", 10, 2 );
function disable_currency_validation_get_price( $price, $price_raw ) {
    return $price_raw;
}