[Tickets #14011] filename becomes ???.txt if not English of .txt

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Ticket URL: https://bugs.horde.org/ticket/14011
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  Ticket             | 14011
  Created By         | nethubonline at gmail.com
  Summary            | filename becomes ???.txt if not English of .txt
  Queue              | IMP
  Version            | 6.2.8
  Type               | Bug
  State              | Unconfirmed
  Priority           | 1. Low
  Milestone          |
  Patch              |
  Owners             |
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nethubonline at gmail.com (2015-06-12 06:28) wrote:

if I compose new email and attach a file with non English characters  
(e.g.: ????.txt / ??.txt) , the attachment filename will be changed to  
???.txt

This only happen for .txt file, but no problem for .png

Even I just save it in draft, it is also ???.txt

Below is part of mail source, you can see .png is using utf-8 but .txt  
is using us-ascii, I think it is the core problem.

--=_niDwCrm6H6ppSnSrbXnJVqo
Content-Type: text/plain; name*=us-ascii''%3F%3F%3F%3F.txt
Content-Disposition: attachment; size=10;
  filename*=us-ascii''%3F%3F%3F%3F.txt

fjskafjsal
--=_niDwCrm6H6ppSnSrbXnJVqo
Content-Type: image/png;
  name*=utf-8''%E3%82%81%E3%81%BE%E3%81%97%E3%81%A6.png
Content-Disposition: attachment; size=7736;
  filename*=utf-8''%E3%82%81%E3%81%BE%E3%81%97%E3%81%A6.png
Content-Transfer-Encoding: base64