How to decode a (percent encoding URL) that contains Arabic characters?

If you want to do it manually, you'll have to write a function with UTF-8 support. However, there's an easier way which is to rely on the JScript engine using an MSScriptControl.ScriptControl object. You could use the function from this answer.

Here's a complete example:

Public JSEngine

Public Sub InitializeJSEngine()
    Set JSEngine = CreateObject("MSScriptControl.ScriptControl")
    JSEngine.Language = "JScript"
End Sub

Function UrlDecode(s) As String
    UrlDecode = Replace(s, "+", " ")
    UrlDecode = JSEngine.CodeObject.decodeURIComponent(UrlDecode)
End Function

Private Sub Form_Load()
    ' Make sure this is called before calling `UrlDecode`.
    InitializeJSEngine
End Sub

Private Sub btnDecode_Click()
    ' Prints: "دشمني در اعماق-2019-12-09 01:09:00"
    ' ..which is Persian, not Arabic ;‑)
    Debug.Print UrlDecode("%D8%AF%D8%B4%D9%85%D9%86%DB%8C+%D8%AF%D8%B1+%D8%A7%D8%B9%D9%85%D8%A7%D9%82-2019-12-09+01%3A09%3A00")
End Sub