First Script

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using TMPro;

public class DialogueWindow : MonoBehaviour
{
    public const float kMaxTextTime = 0.1f;
    public static int TextSpeed = 2;

    public TMP_Text Text;
    public string CurrentText;

    protected enum TextStateType
    {
        None,
        Writing,
        Waiting
    }

    TextStateType TextState;

    CanvasGroup Group;

    private void Start()
    {
        Group = GetComponent<CanvasGroup>();
        Group.alpha = 0;
    }

    public void Show(string dialogue)
    {
        CurrentText = dialogue;
        StartCoroutine(DisplayText());
        Group.alpha = 1;
    }

    public void Close()
    {
        Group.alpha = 0;
        Text.text = "";
        TextState = TextStateType.None;
    }

    protected IEnumerator DisplayText()
    {
        Text.text = "";
        TextState = TextStateType.Writing;

        foreach (char c in CurrentText.ToCharArray())
        {
            Text.text += c;

            yield return new WaitForSecondsRealtime(kMaxTextTime / TextSpeed);
        }

        TextState = TextStateType.Waiting;

        yield return null;
    }
}