Sub Feuil5_Bouton1_Clic()
Application.ScreenUpdating = False
Dim Plg As Range, T(), Mois(), L As Long, n As Byte
Set Plg = Range("D10", Cells(Rows.Count, 4).End(xlUp))
T = Plg
Mois = Array("", "jan", "feb", "mar", "apr", "may", "jun", "jul", "aug", "sep", "oct", "nov", "dec")
For L = 1 To UBound(T, 1)
For n = 0 To 12
If Trim(T(L, 1)) = Mois(n) Then T(L, 1) = n: Exit For
Next
Next
Plg = T
End Sub