The best way is to study the example version. In the example prolog.ps, two routines need to be written, makecodeset12 and makeEUCfont. Makecodeset12 sets up local font encoding information. This routine might differ from locale to locale. MakeEUCfont combines the base font and the locale font to form a composite font. The creator of the prolog file should have good knowledge of PostScript in order to write makecodeset12 and makeEUCfont.
prolog.ps file support is kept for backward compatibility only. Do not create a new prolog.ps file for the printing needs of a locale. Use mp.conf instead.