Friendly tip to avoid messed up galleries:

1) put all pictures from same set into a random folder
2) Ctrl+A to select all
3) right click to 1st picture and select rename
4) type in name and press enter
5) you'll now have files name(1), name(2).....name(100)

If we downloaded the messed up gallary, then I think the only way to fix it would be manual sorting, although I would also appreciate it if someone proves me wrong by letting us know of a script to sort by last character.

Base +14, blackhadess32 +3, Thira -23, kakak +6, Tposat +5, oo123777 -6

How to reorder the pictures:
1. Put all pics in a folder.
2. Search for "_5.jpg".
3. Select all, press [F2] to rename to Set5
4. Back. Search for "_4.jpg".
5. Select all, press [F2] to rename to Set4
6. Repeat 4-5, until all pictures got new names.

Base +6, Tposat +5, oo123777 +6