Comment 46 for bug 1599516

…and finally found how to fix in 14.04 too !

Helped by the command provided by bertrand0

dpkg-query -S \*/{translations,locale,locales,locale-langpack,i18n} | sed -r 's/, /\n/g' | sed -r 's/:.*//' | sort -u | sudo xargs aptitude reinstall

I've finally noticed that xkb-data and xkb-data-i18n were not at their initial trusty version. Months ago I had manually upgraded them to fix a problem with somehow inactive Right Ctrl key. So I've forced back those packages to their actual trusty version, and now accented letters are back in title bars, dash and hud ( after relogging ).