The only latin-script based languages I know that use some accentuated letters not existing in precomposed form in unicode are Guarani (it uses "g with tilde") and Chechen (it uses several letters with a dot above, some exist in precomposed, but others don't).
There may be others, but I only know about those two.
-- Linux-UTF8: i18n of Linux on all levels Archive: http://mail.nl.linux.org/linux-utf8/