rfc2388 doesn't care about the encoding of strings despite of returning them.
The result of a parsed body that doesn't contain binary data is then a vector of octets disguised as string, forcing the ultimate user to jump through this or a similar hoop:
(sb-ext:octets-to-string (map '(vector (unsigned-byte 8)) #'char-int s))
Hunchentoot for example will just return this broken string when rfc2388 is used for parsing a parameter's content.
IMO parse-mime should return a vector of octets and not a string. Its users (e.g. HT) should then apply appropriate character conversion functions to build a proper string.
Leslie