plpgsql setof help

Hello, I'm trying to write a pl/pgsql function that takes in a column 
(setof?) of text values and returns an english language list, for example:

if "select towns from towns_table;" retuned
town1
town2
town3

I want the following:
select column_to_english_list( select towns from towns_table );

to return:
'town1, town2 and town3'

In order to do this, I think I would have to create a pl/pgsql function 
that accpts a setof text argument, but I'm not sure that's allowed.  
Anyone care to comment?

Thank you,

Matthew O'Connor