Since so many people mentioned their longest multi-segment trips, mine was as follows:
For those who don't know airport codes,
that was Boston-New York-Vancouver-Hong Kong-Denpasar, Indonesia (Bali). Total travel time (including the horrible waits in terminals) was 32hrs 15mins.
I recall that when I arrived in Bali, for some strange reason, I could not comprehend the signage. I could read them but I could not comprehend! ....and yes, they were in ENGLISH!