Selecione as células que você deseja converter e execute esta macro curta:
Sub dural()
Dim dy As Long, mnth As Long, yr As Long
Dim t As String, U As Long, d As Date
Dim r As Range
bry = Split("Januar,Februar,März,April,Mai,Juni,Juli,August,September,Oktober,November,Dezember", ",")
For Each r In Selection
t = r.Text
ary = Split(t, " ")
U = UBound(ary)
yr = CLng(ary(U))
dy = CLng(ary(U - 1))
For i = 0 To 11
If ary(U - 2) = bry(i) Then
mnth = i + 1
End If
Next i
d = DateSerial(yr, mnth, dy)
r.Value = d
Next r
End Sub
Em seguida, aplique a formatação desejada aos valores resultantes.
EDIT # 1:
Para usar essa conversão como uma função (UDF ()) , use o seguinte código:
Public Function EngDate(inpt As String) As Date
Dim dy As Long, mnth As Long, yr As Long
Dim t As String, U As Long, d As Date
bry = Split("Januar,Februar,März,April,Mai,Juni,Juli,August,September,Oktober,November,Dezember", ",")
t = inpt
ary = Split(t, " ")
U = UBound(ary)
yr = CLng(ary(U))
dy = CLng(ary(U - 1))
For i = 0 To 11
If ary(U - 2) = bry(i) Then
mnth = i + 1
End If
Next i
d = DateSerial(yr, mnth, dy)
EngDate = d
End Function