Custom encodings, as was standard (or, well, mandatory) before Unicode (1991). Hell, Dyalog APL to this day supports its classic 1-byte-per-char encoding (not e

Custom encodings, as was standard (or, well, mandatory) before Unicode (1991). Hell, Dyalog APL to this day supports its classic 1-byte-per-char encoding (not even ASCII-compatible! Nor EBCDIC!) in addition to Unicode. Looks like the APL chars were added in Uncicode 1.1 (1993), two years after 1.0, which is quick enough.