add vietnamese to changelog
add vietnamese to changelog

lyw07/kolibri,learningequality/kolibri,lyw07/kolibri,indirectlylit/kolibri,lyw07/kolibri,learningequality/kolibri,lyw07/kolibri,indirectlylit/kolibri,mrpau/kolibri,learningequality/kolibri,mrpau/kolibri,mrpau/kolibri,indirectlylit/kolibri,mrpau/kolibri,indirectlylit/kolibri,learningequality/kolibri