And according to "DuckDuckGo Hiring" page, the DuckDuckGo search engine still uses Perl 5 in their backend.

See also the little-known website Booking.com

booking uses Perl? that's one of the web sites that gives me the irrational "the backend must be Java" feeling. can't explain why though.

Got curious. Seems like they have been a heavy Perl shop from the beginning.

Their backend developer job ads appear to be oddly programming language neutral which I assume means they're still using Perl a lot. (Been there, done that, when recruiting for work in an unusual programming language.)

I don't think they're comparable... I read stories on how a paid reservation at Booking.com isn't a guaranteed stay at a hotel. Geizhals gives you the stock and availability infos right on the results page. Seems like one is making better use of Perl that the other.