Looking at the list of pending tag synonym suggestions that I'm allowed to vote on, I see 50 or so entries. Most of them have been there for months, waiting for the yay or nay. To get to that screen, you have to get through a rather baroque sequence of clicks.
I'm wondering if synonym suggestions should be better promoted, perhaps from the moderation tools screen. Hopefully this will clear the backlog.
It will also run the risk of more bad synonyms getting through, but if that's the case, then the voting mechanism needs revisiting.