I would like the text "On %a, %Y-%m-%d at %H:%M, %%s wrote:" prepended to
quoted material to be customizable.

Rationale: The text translated for my locale (fr_FR) is illegible to most
of my recipients. Moreover, and more importantly, it contains characters
absent in ISO 8859-2 (most of my mails are in Polish), thus generating
UTF-8 mails (which many mailers can't process properly).

A workaround is to change the locale or to cut the line away every time I
reply.