Language language = Language.getInstance();
            setScreen(new MessageScreen(language.getElement("connect.notready")));
            int port = ServerLauncher.getAvailablePort();
            server.startServer(levelId, port);  // Lengthy call that sleeps once a second

------------

package net.minecraft.client.gui;

import net.minecraft.locale.Language;

public class MessageScreen extends Screen {
    String message;

    public MessageScreen(String message) {
        this.message = message;
    }

    @Override
    public void render(int xm, int ym, float a) {
        renderBackground();


        drawCenteredString(font, message, width / 2, height / 2 - 10, 0xffffff);

        super.render(xm, ym, a);
    }

}