bibtex-progress-message is a compiled Lisp function in `bibtex.el'.

(bibtex-progress-message &optional FLAG INTERVAL)

Echo a message about progress of current buffer.
If FLAG is a string, the message is initialized (in this case a
value for INTERVAL may be given as well (if not this is set to 5)).
If FLAG is `done', the message is deinitialized.
If FLAG is nil, a message is echoed if point was incremented at least
`bibtex-progress-interval' percent since last message was echoed.