First I would charge 2-2.5x as much vs a standard window to cover the additional labor time. Typically I will start on the interior as I would have to remove the screen first. What I do is open the louvres until they are nearly perpendicular or fully open. I will take my 25cm mop and run it back and forth under the glass piece and then do the same with a 25cm or smaller squeege. Then I take a basic cotton terry cloth rag and wipe from out to in along the two metal edges to collect any water remaining. As for the exterior, WFP if possible, but if trad is your only option, I close the window back down so that you can still get your squeege channel the full width of the louvre yet you csn run the mop side to side to soap multiple piecese simultaneously.
Unfortunately, just like French panes, there is no other option than to clean each piece individually. In that instance Luke advised to cut an extra channel down to the exact width of the French pane, then run your dry finger along the top edge of the pane before placing the rubber at the top for a single straight pull down.
I guess you could do the same for the metal mount edge. Wipe the edge with a dry finger before placing the rubber.