how to write a vba code to remove and replace UTF8-Characters

I have this code and I still can't seem to replace non English characters like Vietnamese or Thai from my data with a simple "placeholder".

Sub NonLatin()
Dim cell As Range
    For Each cell In Range("A1", Cells(Rows.Count, "A").End(xlUp))
        s = cell.Value
            For i = 1 To Len(s)
                If Mid(s, i, 1) Like "[!A-Za-z0-9@#$%^&* * ]" Then cell.Value = "placeholder"
            Next
    Next
End Sub

Appreciate your help