Comment 45 for bug 1599516

16.04 → get back to normal situation ( with accented letters ) thanks to Bertrand0 here https://forum.ubuntu-fr.org/viewtopic.php?pid=21586183#p21586183
which also confirms BleachBit is to blame.

sudo aptitude reinstall apt chromium-browser chromium-browser-l10n cups-common dconf-editor debconf-i18n dpkg e2fsprogs example-content firefox firefox-locale-fr fwupdate gimp-data gimp-plugin-registry gksu gnome-icon-theme gstreamer1.0-plugins-bad gstreamer1.0-plugins-ugly iso-codes language-pack-fr language-pack-fr-base language-pack-gnome-fr language-pack-gnome-fr-base language-selector-common libapt-inst2.0 libapt-pkg5.0 libc-bin libgimp2.0 libgksu2-0 libgom-1.0-common liboxideqtcore0 libqt4-script libstdc++-5-dev libx11-data libzvbi-common locales menu pavucontrol qtcore4-l10n qttranslations5-l10n radiotray synaptic unity-lens-applications unity-lens-files unity-tweak-tool update-notifier-common vlc-data xdg-user-dirs xkb-data-i18n xscreensaver

I'm still struggling with 14.04…