Summary

MS950 charset encoder behaves differently as defined in the Traditional Chinese Windows specification

Problem

Windows code page 950 has some n:1 byte-to-char mappings for certain code points. In JDK's MS950 charset, there are 4 char-to-byte mappings differ from Traditional Chinese Windows.
(Actual issue was in https://bugs.openjdk.java.net/browse/JDK-8232161)

Solution

I recommend that following 4 char-to-byte mappings need to change.

Before:

\u2550 -> \xA2\xA4
\u255E -> \xA2\xA5
\u2561 -> \xA2\xA7
\u256A -> \xA2\xA7

After:

\u2550 -> \xF9\xF9
\u255E -> \xF9\xE9
\u2561 -> \xF9\xEB
\u256A -> \xF9\xEA

Definition:
Traditional Chinese Windows conversion table is:
https://unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WINDOWS/CP950.TXT
Newer MS950 definition is:
https://unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WindowsBestFit/bestfit950.txt

\u2550, \u255E, \u2561 and \u256A are in BOX DRAWINGS Unicode range.
(See attached 4Chras.png for font glyphs)

Specification

N/A