I have a test profile in my forum that is set for Spanish (even though my Spanish is close to non-existent any more) and I noticed that it does show the day before the month.
The official language of the TSI forum is U.S. English, however when I post admin announcements that have a date, I use a format of a two-digit day# + dash + month name + dash + four-digit year#, e.g. 25-May-2015. I figure that about everybody ought to be able to figure that out.
Of course that’s longer than is needed for the topic list, and also doesn’t take into account the formatting flexibility of localization.