About [[Europeana:Date.formats.long/en]]

See http://ruby-doc.org/core-2.0/Time.html#method-i-strftime

%d - Day of the month, zero-padded (01..31)
%B - The full month name (January)
%Y - Year with century (can be negative, 4 digits at least)

Many thanks for these explanations! Indeed I guessed what d and Y stand for but B waswuite mysterious to me.

I will try to add this to the documentation of the message.