From the logs it seems that even if the locale is set to a non-english language, the config variable xkb-keymap introduced in 17.10 is set to 'us' and Ubiquity uses this value to update the UI.
Apr 17 08:55:11 debconf (filter): <-- GET debian-installer/locale
debconf (developer): <-- GET debian-installer/locale
debconf (developer): --> 1 fr_FR.UTF-8
Apr 17 08:55:11 debconf (filter): <-- GET localechooser/languagelist
debconf (developer): <-- GET localechooser/languagelist
debconf (developer): --> 1 fr
Apr 17 08:55:11 debconf (filter): <-- GET debian-installer/country
debconf (developer): <-- GET debian-installer/country
debconf (developer): --> 1 FR
Apr 17 08:55:11 debconf (filter): <-- GET keyboard-configuration/xkb-keymap
debconf (developer): <-- GET keyboard-configuration/xkb-keymap
debconf (developer): --> 1 us
Apr 17 08:55:11 debconf (filter): <-- GET keyboard-configuration/modelcode
debconf (developer): <-- GET keyboard-configuration/modelcode
debconf (developer): --> 1
Apr 17 08:55:11 debconf (filter): <-- GET keyboard-configuration/layoutcode
debconf (developer): <-- GET keyboard-configuration/layoutcode
debconf (developer): --> 1
Apr 17 08:55:11 debconf (filter): <-- GET keyboard-configuration/variantcode
debconf (developer): <-- GET keyboard-configuration/variantcode
debconf (developer): --> 1
Apr 17 08:55:11 debconf (filter): <-- GET keyboard-configuration/optionscode
debconf (developer): <-- GET keyboard-configuration/optionscode
debconf (developer): --> 1
From the logs it seems that even if the locale is set to a non-english language, the config variable xkb-keymap introduced in 17.10 is set to 'us' and Ubiquity uses this value to update the UI.
Apr 17 08:55:11 debconf (filter): <-- GET debian- installer/ locale installer/ locale languagelist languagelist installer/ country installer/ country configuration/ xkb-keymap configuration/ xkb-keymap configuration/ modelcode configuration/ modelcode configuration/ layoutcode configuration/ layoutcode configuration/ variantcode configuration/ variantcode configuration/ optionscode configuration/ optionscode
debconf (developer): <-- GET debian-
debconf (developer): --> 1 fr_FR.UTF-8
Apr 17 08:55:11 debconf (filter): <-- GET localechooser/
debconf (developer): <-- GET localechooser/
debconf (developer): --> 1 fr
Apr 17 08:55:11 debconf (filter): <-- GET debian-
debconf (developer): <-- GET debian-
debconf (developer): --> 1 FR
Apr 17 08:55:11 debconf (filter): <-- GET keyboard-
debconf (developer): <-- GET keyboard-
debconf (developer): --> 1 us
Apr 17 08:55:11 debconf (filter): <-- GET keyboard-
debconf (developer): <-- GET keyboard-
debconf (developer): --> 1
Apr 17 08:55:11 debconf (filter): <-- GET keyboard-
debconf (developer): <-- GET keyboard-
debconf (developer): --> 1
Apr 17 08:55:11 debconf (filter): <-- GET keyboard-
debconf (developer): <-- GET keyboard-
debconf (developer): --> 1
Apr 17 08:55:11 debconf (filter): <-- GET keyboard-
debconf (developer): <-- GET keyboard-
debconf (developer): --> 1