** If you specify --unibyte when starting Emacs, then all buffers are
unibyte, except when a Lisp program specifically creates a multibyte buffer. Setting the environment variable EMACS_UNIBYTE has the same effect. The --no-unibyte option overrides EMACS_UNIBYTE and directs Emacs to run normally in multibyte mode.
The option --unibyte does not affect the reading of Emacs Lisp files, though. If you want a Lisp file to be read in unibyte mode, use -*-unibyte: t;-*- on its first line. That will force Emacs to read that file in unibyte mode regardless of how Emacs was started.