option to parse two consecutive numbers without adding them together

[0xgeert]

Is there an option to have the parser return readInt("nine hundred and twelve forty five") = -1, since it's not a valid number instead of adding the two numbers together, i.e.: 912 + 45 ?

If not, any pointers on where I might add this best in the code?

[nmussy]

I can't see how to make this an easy fix. You'd have to change the basic behavior of the parser. The algorithm is meant to be "dumb, but effective," and doesn't have a way to report complex errors like this.

I can go into further details if you'd like, but if you've gone through a bit of the code, you'll see that it operates around "levels" of numbering (e.g. one is level 0, 10 is level 1, 100 is level 2 etc.), and uses those levels to multiple and add numbers recursively.
That way, sixty six hundred and twenty five is interpreted, level-wise, as (((1 + 0) * 2) + 1) + 0. I don't see how I could add a logic of right and wrong ordering of those levels without breaking its modularity.

Your example is especially bothersome because it contains an exception, twelve, which is stored at the zeroth level of the locale (exception as in not twoteen, like you have starting thirteen).

The locales don't include a syntactic check, which would be much more complicated to implement. They only contain a loose interpretation of number tokens and how to add or multiply them.