Access serialized values from an outside script,Custom Editor Values access on Play

Hello I am trying to make a script using a custom inspector and I think I don't understand the serialization part of all of it. This is the first time I do this so I am a beginner.

Main class is this :

 [System.Serializable]
 public class LanguageManager : MonoBehaviour {
 
   private static LanguageManager instance = null;
 
   public static LanguageManager Instance
   {
     get
     {
       if (instance == null)
       {
         instance = new LanguageManager();
       }
       return instance;
     }
   }
 
   [System.Serializable]
   public class LanguageMainClass
   {
     public string language;
     public Sprite flag;
     public string path;
     public bool isDefault;
     public bool isSelected;
   }
 
   [SerializeField]
   public List<LanguageMainClass> listOfLanguages;
 
   [SerializeField]
   private AudioLanguageScriptableObject languageObject;
 
   public AudioLanguageScriptableObject LanguageObject
   {
     get
     {
       return languageObject;
     }
     set
     {
       languageObject = value;
     }
   }

Editor is this :

 [ExecuteInEditMode]
 [CustomEditor(typeof(LanguageManager))]
 public class LanguageManagerEditor : Editor {
 
   ReorderableList languageListReorderable;
 
   SerializedProperty languageObject;
 
   private string pathToUse;
 
   void OnEnable()
   {
     languageListReorderable = new ReorderableList(serializedObject.FindProperty("listOfLanguages"));
     languageObject = serializedObject.FindProperty("languageObject");
   }
 
   public override void OnInspectorGUI()
   {
     serializedObject.Update();
 
 
     GUILayout.Label("Create an object to store all your voice clips for each language", EditorStyles.boldLabel);
 
     if (GUILayout.Button("Create a Scriptable Object"))
     {
       LanguageManager.Instance.CreateMyScriptableObject();
     }
 
     GUILayout.Label("Languages List :", EditorStyles.boldLabel);
 
     languageListReorderable.DoLayoutList();
 
     languageListReorderable.GetItem(0).FindPropertyRelative("isDefault").boolValue = true;
     for (int i = 1; i < languageListReorderable.Length; i++)
     {
       languageListReorderable.GetItem(i).FindPropertyRelative("isDefault").boolValue = false;
     }
 
     for (int i = 1; i < languageListReorderable.Length; i++)
     {
       if (languageListReorderable.GetItem(i).FindPropertyRelative("isSelected").boolValue)
         pathToUse = languageListReorderable.GetItem(i).FindPropertyRelative("path").stringValue;
       else
         pathToUse = languageListReorderable.GetItem(0).FindPropertyRelative("path").stringValue;
     }
 
     languageObject.objectReferenceValue = Resources.Load<AudioLanguageScriptableObject>(pathToUse);
 
     GUILayout.Label("Currently using :", EditorStyles.boldLabel);
 
     EditorGUILayout.PropertyField(languageObject);
     EditorUtility.SetDirty(this);
     serializedObject.ApplyModifiedProperties();
   }
 }

The thing is working very well but I can't access any of it from outside, everything returns null no matter what I try.

Thank you for your help.