$ LANG=de_DE date --rfc-822 Don, 3 Mai 2001 16:43:55 +0200 RFC 822 (and the successor 2822) is clear that only english words for day and month are valid. So date should never use i18n maps if -R/--rfc-822 is used because it generates non-compliant date strings.
Fixed in 2.0-14.