char-displayable-p is an autoloaded compiled Lisp function in `mule-util.el'.

(char-displayable-p CHAR)

Return non-nil if we should be able to display CHAR.
On a multi-font display, the test is only whether there is an
appropriate font from the selected frame's fontset to display
CHAR's charset in general. Since fonts may be specified on a
per-character basis, this may not be accurate.