I have used a thin strip of a light weight leather as a splint with good success.
I cut the light weight stuff just as wide as the strap I wanted to repair...and actually glued
it to the back of the strap on either side of the original straps break. I glue the splint rough side down so it matches the rough side on the back of the original strap...I use a flexable, clear drying white glue made for fabrics and crafting...its also a plus if you have a light weight leather thats close in color to the original strap, though the colors can be matched up a bit after the splint has been glued on and dried....
After that, a few stitches can be sewn through the original strap and the splint behind it. Use a fine needle, and a single strand or ply of dark colored, waxed linen cord...dont try to necessairly sew the break together, but rather to attach the splint to the strap....to do that, push the point of the needle through both the strap and splint about an eight of an inch from the break, and close to the edge of the strap...(note, if the strap starts to crumble, stop, it may be too dry rotted to accept even a fine needle?) pull the thread through and whip stitch over the edge with a single stitch ( If the strap will stand it, you can push the needle back through the same hole two or even three times to double or triple up the stitch using that same single hole.) Tie off the thread, and snip it off....repeat three more times, anchoring the splint on either side of the break on both the left and right sides of the strap...then rub a dab of glue into the thread to further secure it.
Its harder to describe than do...and oh yeah, dont hang the bag by its strap even for display or it will most likely eventually break again given time.
TCA
