I have only the english language installed (and so not much experience with multiple language set ups), so hard to verify what I am writing below. But I am hoping it will lead you to some sort of solution.
In any case, the check routines are in a FUNCTION file called tfcmg0005 (Decode Amounts). (I could not find tcmcsdll0006 in my installation - maybe it is not available in BAAN IV c3 A&D). From what I can see, this function script has decodes which rely on messages, which of course are by language. For example, the following gets the word 'hundred':
decode.hundred = form.text$("tfcmgs0186")
Similar code exists for decoding the numbers: 1 to 'one' and so on, using form.text$() command.
SO, if it is possible for you to test this somehow, you could get away with just copying the required messages from english to spanish and translating the words in Maintain Messages. Not sure how you can 'force' the check report to pick the language you need, though. Also, not sure how exactly the number in words will look like in the other language, because the 'assembly' of the words is basically in english. Will need lot of testing, if the concept works.