Edge browser (build 10166) cannot parse parameter value character set and language information: RFC2231

From https://tools.ietf.org/html/rfc2231#section-4:

   Asterisks ("*") are reused to provide the indicator that language and
   character set information is present and encoding is being used. A
   single quote ("'") is used to delimit the character set and language
   information at the beginning of the parameter value.
e.g. Content-Disposition  attachment; filename*= UTF-8''Regional.twbx
Edge seems to ignore the filename and uses a filename based on the url instead. 
How are character sets supposed to be provided for Edge?