Why Doesn’t Transition Animation Work in Nav and Div Elements [duplicate]

var Lang;


setTimeout(function() {
  document.getElementById("SelectLanguage-text").style.filter = "opacity(100%)";
  document.getElementById("SelectLanguage-text").style.top = "0";
  document.getElementsByClassName("EN")[0].style.display = "block";
  document.getElementsByClassName("AR")[0].style.display = "block";
}, 1000);
setTimeout(function() {
  document.getElementById("SelectLanguage-text-ar").style.filter = "opacity(100%)";
  document.getElementById("SelectLanguage-text-ar").style.top = "0";
  document.getElementsByClassName("EN")[0].style.filter = "opacity(100%)";
  document.getElementsByClassName("EN")[0].style.top = "0";
}, 1100);
setTimeout(function() {
  document.getElementsByClassName("AR")[0].style.filter = "opacity(100%)";
  document.getElementsByClassName("AR")[0].style.top = "0";
}, 1200);

document.getElementsByClassName("AR")[0].onclick = function() {
  Lang = "AR";
  Start();
}
document.getElementsByClassName("EN")[0].onclick = function() {
  Lang = "EN";
  Start();
}
document.getElementById("Switch").onclick = function() {
  if (Lang == "AR") {
    Lang = "EN";
    Start();
  } else {
    Lang = "AR";
    Start();
  }
}

document.getElementById("Return").onclick = function() {
  location.reload();
}

function Start() {
  document.getElementById("select-language").style.filter = "opacity(0%)";
  setTimeout(function() {
    document.getElementById("select-language").style.display = "none";
    document.getElementById("AllOtherSects").style.display = "block";
    document.getElementById("AllOtherSects").style.filter = "opacity(100%)";
    document.getElementById("AllOtherSects").style.top = "0";
    document.getElementsByTagName("nav")[0].style.display = "flex";
    document.getElementsByTagName("nav")[0].style.filter = "opacity(100%)";
  }, 500)

  if (Lang == "AR") {
    document.getElementsByTagName("nav")[0].style.direction = "rtl";
    document.getElementsByTagName("nav")[0].style.textAlign = "right";
    document.getElementsByTagName("h1")[0].innerHTML = "تعلم البرمجة";
    document.getElementsByTagName("h1")[0].style.fontFamily = "Arabic";
    document.getElementsByTagName("a")[0].innerHTML = "الرئيسية";
    document.getElementsByTagName("a")[1].innerHTML = "عن";
    document.getElementsByTagName("a")[2].innerHTML = "اتصل بنا";
    document.getElementsByTagName("h1")[3].innerHTML = "تعلم البرمجة";
    document.getElementById("OR").innerHTML = "أو";
    document.getElementById("Switch").innerHTML = "تبديل اللغة";
    document.getElementById("Return").innerHTML = "العودة للتحديد";
  } else {
    document.getElementsByTagName("nav")[0].style.direction = "ltr";
    document.getElementsByTagName("nav")[0].style.textAlign = "left";
    document.getElementsByTagName("h1")[0].innerHTML = "Learn Code";
    document.getElementsByTagName("h1")[0].style.fontFamily = "Title";
    document.getElementsByTagName("a")[0].innerHTML = "Home";
    document.getElementsByTagName("a")[1].innerHTML = "About";
    document.getElementsByTagName("a")[2].innerHTML = "Contact";
    document.getElementsByTagName("h1")[3].innerHTML = "Learn Code";
    document.getElementById("OR").innerHTML = "OR";
    document.getElementById("Switch").innerHTML = "Switch Language";
    document.getElementById("Return").innerHTML = "Return To Setup";
  }
}

@font-face {
  font-family: Title;
  src: url(Fonts/cream_beige/Cream Beige.ttf);
}

@font-face {
  font-family: Arabic;
  src: url(Fonts/Rubik/static/Rubik-Regular.ttf);
}

.Flex {
  display: flex;
}


/* to make every div with this class flex*/

* {
  transition: 0.5s;
  font-family: Rubik;
}

body {
  background-image: linear-gradient(rgba(0, 0, 0, 0.57), rgba(0, 0, 0, 0.57)), url("https://i.ytimg.com/vi/PIhVTAdmouw/maxresdefault.jpg");
  background-repeat: no-repeat;
  background-attachment: fixed;
  background-size: cover;
  animation: BackgroundAnimation 20s infinite ease-in-out;
  color: white;
  margin: 0;
  padding: 0;
}

@keyframes BackgroundAnimation {
  0% {
    background-position: left;
  }
  50% {
    background-position: right;
  }
  100% {
    background-position: left;
  }
}

section {
  height: 100vh;
}

nav {
  padding: 20px;
  display: none;
  filter: opacity(0);
  align-items: center;
  position: fixed;
  width: 100%;
}

nav h1 {
  margin: 10px;
  font-size: xx-large;
  font-family: Title;
  font-weight: 100;
}

nav a {
  margin: 0 20px;
  font-size: 20px;
}

a {
  text-decoration: none;
  color: white;
}

#select-language {
  height: 97vh;
  width: 100%;
  text-align: center;
  align-content: center;
}

#SelectLanguage-text {
  margin-bottom: 0;
  position: relative;
  top: 30px;
  filter: opacity(0);
}

#SelectLanguage-text-ar {
  letter-spacing: 2px;
  margin-top: 0;
  position: relative;
  top: 30px;
  filter: opacity(0);
  font-family: Arabic;
}

#select-language button {
  background-color: rgba(0, 0, 0, 0.61);
  color: white;
  border: 10px white solid;
  padding: 20px 70px;
  font-size: large;
  margin: 20px;
}

#select-language button:hover {
  /*padding: 30px 100px;*/
  transform: scale(1.2);
}

.AR,
.EN {
  top: 30px;
  display: none;
  position: relative;
  filter: opacity(0);
}

#AllOtherSects {
  display: none;
  position: relative;
  filter: opacity(0);
  top: 30px
}

#S1 {
  color: white;
  text-align: center;
  align-content: center;
}

#S1 h1 {
  font-size: 100px;
}

.transparent {
  background-color: transparent;
  border: none;
  color: white;
  font-size: large;
  margin: 20px;
}

.transparent:hover {
  /*padding: 30px 100px;*/
  transform: scale(1.2);
}

<!DOCTYPE html>
<html>

<head>
  <title>Home</title>
  <link rel="stylesheet" href="style.css">
  <link rel="preconnect" href="https://fonts.googleapis.com">
  <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
  <link href="https://fonts.googleapis.com/css2?family=Rubik:ital,wght@0,300..900;1,300..900&display=swap" rel="stylesheet">

</head>

<body>
  <nav>
    <img src="Images/code-slash.svg" alt="">
    <h1>Learn Code</h1>
    <a href="Home.html">Home</a>
    <a href="About.html">About</a>
    <a href="Contact.html">Contact</a>
  </nav>
  <section id="select-language">
    <h1 style="font-size: 40px; font-weight: 300;" id="SelectLanguage-text">Select Language</h1>
    <h1 style="font-size: 40px; font-weight: 300;" id="SelectLanguage-text-ar">اختر اللغة</h1>
    <div class="Flex" style="justify-content: center; flex-wrap: wrap;">
      <button class="AR" onclick="">العربية</button>
      <button class="EN" onclick="">English</button>
    </div>
  </section>
  <div id="AllOtherSects">
    <section id="S1">
      <h1>The Coding</h1>
      <button id="Switch" class="transparent">Switch Language</button><label id="OR"> OR </label><button id="Return" class="transparent">Return To Setup</button>
    </section>
  </div>
  <script src="Script.js"></script>
</body>

</html>