A user on the forum reported that Google is no longer present as a default search engine option in Tor Browser 11.5. tobrop and I have narrowed it down to 11.0.10, which is the first stable release in which it's missing.
I can't see anything that would explain it in the changelog for 11.0.10 however, so I'm guessing it's a bug.
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iirc Mozilla added new localization, so Firefox went looking for our other supported locales which it then couldn't find so it just fell over completely