Server.getLocale returns en_us even if player is using a different locale.

For testing purposes, and to make sure that there is no intereference with other plugins, I made a new server with only one plugin (see attachment) with the following code:

public void onEnable() {
  Bukkit.getScheduler().scheduleSyncRepeatingTask(this, new Runnable() {

    @Override
    public void run() {
      for (Player p : Bukkit.getOnlinePlayers()) {
        System.out.println(" - locale of " + p.getName() + " is " + p.getLocale());
      }
    }
  }, 100, 200);
 }

The output is always en_us.

This works fine in 1.15.2 (haven't tested previous versions), giving the selected locale (only the first output after login sometimes is en_us). Locale changes during the game also result in the correct locale shown in 1.15.2 and en_us in 1.16.1.