Variable: selection-coding-system

Coding system for communicating with other programs.

For MS-Windows and MS-DOS:
When sending or receiving text via selection and clipboard, the text
is encoded or decoded by this coding system. The default value is
the current system default encoding on 9x/Me, `utf-16le-dos'
(Unicode) on NT/W2K/XP, and `iso-latin-1-dos' on MS-DOS.

For X Windows:
When sending text via selection and clipboard, if the target
data-type matches with the type of this coding system, it is used
for encoding the text. Otherwise (including the case that this
variable is nil), a proper coding system is used as below:

data-type coding system
--------- -------------
COMPOUND_TEXT compound-text-with-extensions
STRING iso-latin-1
C_STRING no-conversion

When receiving text, if this coding system is non-nil, it is used
for decoding regardless of the data-type. If this is nil, a
proper coding system is used according to the data-type as above.

See also the documentation of the variable `x-select-request-type' how to control which data-type to request for receiving text. The default value is nil.