Sub ResetLeftToRight()

    Dim oSh As Shape
    Dim oSl As Slide

    ' make sure slide sorter reads left to right    
    ActivePresentation.LayoutDirection = ppDirectionLeftToRight

    ' then fix each of the text boxes
    For Each oSl In ActivePresentation.Slides
        For Each oSh In oSl.Shapes
            On Error Resume Next
            If oSh.HasTextFrame Then
                If oSh.TextFrame.HasText Then
                    WIth oSh.TextFrame.TextRange.ParagraphFormat
                         .TextDirection = ppDirectionLeftToRight
                    End With 
                End If
            End If
        Next    ' shape
    Next    ' slide

End Sub