Function fz_encode_character_with_fallback 

pub unsafe extern "C" fn fz_encode_character_with_fallback(
    ctx: *mut fz_context,
    font: *mut fz_font,
    unicode: c_int,
    script: c_int,
    language: c_int,
    out_font: *mut *mut fz_font,
) -> c_int

Find the glyph id for
a given unicode character within a font, falling back to
an alternative if not found.

font: The font to look for the unicode character in.

unicode: The unicode character to encode.

script: The script in use.

language: The language in use.

out_font: The font handle in which the given glyph represents
the requested unicode character. The caller does not own the
reference it is passed, so should call fz_keep_font if it is
not simply to be used immediately.

Returns the glyph id for the given unicode value in the supplied
font (and sets *out_font to font) if it is present. Otherwise
an alternative fallback font (based on script/language) is
searched for. If the glyph is found therein, *out_font is set
to this reference, and the glyph reference is returned. If it
cannot be found anywhere, the function returns 0.