GNU `recode' converts files between character sets and usages.  When
exact transliterations are not possible, it may get rid of the
offending characters or fall back on approximations.  This program
recognizes or produces nearly 150 different character sets and is able
to transliterate files between almost any pair.  Most RFC 1345
character sets are supported.

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There is also a patch avaliable for the bibliographic
character sets: 

	ISO 5426:1983
	Extension of the Latin alphabet coded character set for bibliographic
	information interchange.

	Z39.47-1993 Extended Latin Alphabet Coded Character Set for
	Bibliographic Use (ANSEL)
	[also known as 8-Bit ANSEL, used by USMARC]

See http://www.de.freebsd.org/~wosch/src/recode/
Extract the archive and follow the instructions in README.bib.