set-process-filter-multibyte
set-process-filter-multibyte is a built-in function in `C source code
'.
(set-process-filter-multibyte PROCESS FLAG)
This function is obsolete since 23.1.
Set multibyteness of the strings given to PROCESS's filter.
If FLAG is non-nil, the filter is given multibyte strings.
If FLAG is nil, the filter is given unibyte strings. In this case,
all character code conversion except for end-of-line conversion is
suppressed.