In summary: I don't have any indication it's in current use. I saw this URL in intercepted traffic from an iOS 13 device. I suspect it was used at some point but not anymore. I bet iOS 15 still uses something similar but doesn't use this particular URL (perhaps one with more obscurity/protection).
It's a binary file, but if you look at the hex dump there's a list of vaguely "bad" words near the end including "whorehouse," "Zipperheads," "unabomber". I have no idea what format it is, though.
In summary: I don't have any indication it's in current use. I saw this URL in intercepted traffic from an iOS 13 device. I suspect it was used at some point but not anymore. I bet iOS 15 still uses something similar but doesn't use this particular URL (perhaps one with more obscurity/protection).
p.s. I also found this list of spelling corrections/autocompletes: https://cdn.smoot.apple.com/static/static_corrections_dict/2...
Some examples: