Substitute Excel-Workbook reference for another
Try adding Application.Calculation = xlManual where you turn updating off, and then turn it back to xlAutomatic at the end.

In addition, turn events off (and then on again): Application.EnableEvents = False and Application.EnableEvents = True.

I suspect that everytime you change a file name in a cell, the workbook tries to access the link and update the cell. 

Small point - doesn't affect speed:

If Mid(DateiName, 1, 1) &lt;&gt; "[" Then
    DateiName = "[" &amp; DateiName 
    DateiName = DateiName &amp; "]"
End If


could be

If Mid(DateiName, 1, 1) &lt;&gt; "[" Then
    DateiName = "[" &amp; DateiName &amp; "]"
End If


Instead of Set wb = ActiveWorkbook, you could use ThisWorkbook - it is a little more assertive if that is what you need. I don't have the context on how this function is used, so it may be called when another workbook is active.