"I do not speak French" versus "I do not know how to speak French". Both are correct, though only the latter clarifies not speaking the language because they do not understand it, rather than purely out of spite. So in this specific case, the former could be used as a subtle FU.
"I do not speak French" versus "I do not know how to speak French". Both are correct, though only the latter clarifies not speaking the language because they do not understand it, rather than purely out of spite. So in this specific case, the former could be used as a subtle FU.