Fix translatable string construction

Fix translatable string construction

In a few places, we were constructing translatable strings consisting of
elements list by adding one element at a time and separately a comma.
This is not great from a translation point of view, so rewrite to append
the comma together with the corresponding element in one go.

Author: Peter Smith <smithpb2250@gmail.com>
Author: Álvaro Herrera <alvherre@kurilemu.de>
Discussion: https://postgr.es/m/CAHut+Pvp7jYcaiZ3pXedXgLcWZWDBLXFUK05JtZpGv3Mj=UOjw@mail.gmail.com