Option Explicit
Public Sub ChangeSpellCheckingLanguage()
    Dim j As Integer, k As Integer, scount As Integer, fcount As Integer
    scount = ActivePresentation.Slides.Count
    For j = 1 To scount
        fcount = ActivePresentation.Slides(j).Shapes.Count
        For k = 1 To fcount
            If ActivePresentation.Slides(j).Shapes(k).HasTextFrame Then
                ActivePresentation.Slides(j).Shapes(k) _
                .TextFrame.TextRange.LanguageID = msoLanguageIDEnglishUK
            End If
        Next k
    Next j
End Sub