The translation for "and" appears in the Special:Version page, between the last two items of a list. If a comma is needed, add it at the beginning without a gap between it and the "&".   is a blank space, one character long. Please leave it as it is.
This can also appear in the credits page if the credits feature is enabled,for example the credits of the support page. (To view any credits page type &action=credits at the end of any URL in the address bar.)