Sub CheckLanguage()
Application.ScreenUpdating = False
Dim Rng As Range
For Each Rng In ActiveDocument.Range.SpellingErrors
  With Rng
    If .LanguageID = wdEnglishUK Then
      .LanguageID = wdGerman
      If .SpellingErrors.Count > 0 Then ActiveDocument.Undo
    ElseIf .LanguageID = wdGerman Then
      .LanguageID = wdEnglishUK
      If .SpellingErrors.Count > 0 Then ActiveDocument.Undo
    End If
  End With
Next
Application.ScreenUpdating = True
End Sub