\hyphenation will be flushedFor example
! Improper \hyphenation will be flushed.
\'#1->{
\accent 19 #1}
<*> \hyphenation{Ji-m\'e
-nez}
(in Plain TeX) or
! Improper \hyphenation will be flushed.
\leavevmode ->\unhbox
\voidb@x
<*> \hyphenation{Ji-m\'e
-nez}
in LaTeX.
As mentioned in "hyphenation failures",
words with accents in them may not be hyphenated. As a result, any
such word is deemed improper in a \hyphenation command.
The solution is to use a font that contains the character in question,
and to express the \hyphenation command in terms of that
character; this "hides" the accent from the hyphenation mechanisms.
LaTeX users can be achieved this by use of the fontenc
package (part of the LaTeX distribution). If you select an 8-bit
font with the package, as in \usepackage[T1]{fontenc},
accented-letter commands such as the \'e in
\hyphenation{Ji-m\'e-nez} automatically become the single accented
character by the time the hyphenation gets to look at it.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=badhyph