Comment 12 for bug 1643210

How about using "dn = str(Header(uvia, lcs))" instead of "dn = str(Header(uvia, 'utf-8'))" ?
As variable uvia is always unicode, there is no afraid to be mistaken encodings. Header() treats charset parameter only for a hint, so it uses 'utf-8' as the fall back if it fail to encode to lcs.

test case 1.
  list's language : fr (iso-8859-1)
  sender's language : fr (iso-8859-1)
  sender's display name : =?iso-8859-1?q?G=E9n=E9rales?=
(results)
  From: =?iso-8859-1?q?G=E9n=E9rales_via_Mailman-test?= <...>

test case 2.
  list's language : ja (euc-jp, out going messages are encoded to iso-2022-jp)
  sender's language : ja (euc-jp, out going messages are encoded to iso-2022-jp)
  sender's display name : =?ISO-2022-JP?B?GyRCRnNMWkx3P04bKEI=?=
(results)
  From: =?iso-2022-jp?b?GyRCRnNMWkx3P04bKEIgKE1haWxtYW4tdGVzdCAbJEI3UE0zGyhCKQ==?= <...>

test case 3.
  list's language : en (us-ascii)
  sender's language : en (us-ascii)
  sender's display name : Yasuhito FUTATSUKI
(results)
  From: Yasuhito FUTATSUKI via Mailman-test <...>

test case 4.
  list's language : fr (iso-8859-1)
  sender's language : ja (euc-jp, out going messages are encoded to iso-2022-jp)
  sender's display name : =?UTF-8?B?5LqM5pyoIOmdluS7gQ==?=
(results)
  From: =?utf-8?b?5LqM5pyoIOmdluS7gSB2aWEgTWFpbG1hbi10ZXN0?= <...>

in all of above, it looks fine.