Found by parsing the results from this bash script:
for define in $(grep define *.h |  awk'{print $2}');
do if ! grep -q $define *.c
then
        echo "$define not found";
fi
done

It is not used by any language. There is no need to check for it in
LoadVoice().

The #defines should be renamed to better convey their meaning.

The flag is never set anywhere so the if-clause will always evaluate to false.

When set in a language file, a period followed by a lower case letter is
detected as end of sentence. Normal behavior is to require a capital
letter.

- param2[] is only used to set a second value to LOPT_BRACKET_PAUSE. It is simpler
to have two values in param[] instead. This simplifies the codebase.

- Instead of setting "option bracket X Y" in language files, use
keywords "brackets X" and "bracketsAnnounced Y" instead to follow the
naming convention of other keywords.

- Add missing documentation to docs/voices.md.

There is no code related to it.

It is set but never used.

translate.h gives two settings to LOPT_CAPS_IN_WORD, but only one of them is actually ever used.

It's a duplicate of CTRL_EMBEDDED.

It is set in voices.c but never used. docs/voices.md indicates that the keyword intonation only takes one parameter, confirming that option_tone2 is unused.

these are the only references in the code.