The System Variable ŒMC contains the character used to replace a Unicode or other character which cannot be represented in APLX. By default, it is set to a question mark, but you can set it to any character in ŒAV. It can be localized in the header of a function or method.
See ŒUCS for an example, and for more information on translating to and from Unicode.
Note that, as well as translation using ŒUCS, the character specified in ŒMC is also used when translating Unicode text received anywhere within APLX. This can include Unicode text which has been: