Albert Barnes Commentary Judges 12:6

"then said they unto him, Say now Shibboleth; and he said Sibboleth; for he could not frame to pronounce it right: then they laid hold on him, and slew him at the fords of the Jordan. And there fell at that time of Ephraim forty and two thousand." — Judges 12:6 (ASV)

Shibboleth; and he said Sibboleth - This is a curious instance of dialectal difference of pronunciation between the East and West Jordanic tribes. It is evidence of the sound “sh” having passed into the Hebrew from the East of Jordan, possibly from the Arabians, with whom the sound is common.

Forty-two thousand - The number includes the slain in battle and those killed at the fords.