The ornamental design for a slatedseatingfoldingchair, as shown and described.
FIG. 1 is an front view of the slated seating folding chair;
FIG. 2 is an right side view with the opposite side being a mirror image thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a bottom view thereof;
FIG. 5 is a back view thereof; and,
FIG. 6 is an perspective environmental view of the slated seating folding chair showing our new design. The broken lines in the figure provide environmental structure or boundaries that form no part of the claimed design.