Function fz_text_language_from_string 

pub unsafe extern "C" fn fz_text_language_from_string(
    str_: *const c_char,
) -> fz_text_language

Convert ISO 639 (639-{1,2,3,5}) language specification
strings losslessly to a 15 bit fz_text_language code.

No validation is carried out. Obviously invalid (out
of spec) codes will be mapped to FZ_LANG_UNSET, but
well-formed (but undefined) codes will be blithely
accepted.