Lying. It is called lying, deceit, or bearing false witness.
In my house I do not permit "yeah", or "okay". It is "yes" and anything else is interpreted as a 'no'.
Once you press someone to speak a "yes" as a solid commitment, for example to an understanding of an instruction. If this puts the person on the defensive then you are dealing with someone who is not interested in being held accountable.
This isn't fair, because it's misunderstanding the problem. It's not that they're lying, it's that, in their culture, the meaning of yes is something different, meaning "I hear you" rather than "I understand you". If they're not strong with english they might not have a grasp of this, so (in the case of Mandarin as primary language) you have to usually think of it as an empty "uh huh" type filler word, not a word with actual meaning.
The real problem I have is the "saving face" concept prevents them admitting they don't understand something. This is where the "high context" part comes in. You can't listen to what they say directly, you have to go off how they say it, and other context clues. This is what I have the biggest problem with. The only way to know if they actually understand something is test their understanding, like have them repeat/explain it back to you. From a low context/western perspective, this results in low verbal trust (because it technically is). I've wasted so many hours on taking something said at face value, that I just default to verifying everything that's said, and trying to be patient when I find out the truth. But, I am getting much better at reading the cues, so can usually spot when the (from my western/low context perspective) bullshit when it starts.
There are old stereotypes around this clash of meaning/culture, but it really is just that. If you're from their culture, and speak their language, there's no "bullshitting" or "lying". From what I've been told, it's incredibly clear when someone is saving face, and it's very clear what the response should be, to "help" them save face. Westerners are, literally, just blind to it all. It's an incompatible mindset and language/expression that requires a robust translation layer that needs to exist in one of the parties. I seem to be mostly incapable of high context communication, even in english, so I'm just as "at fault" in the two party role of communication.
I live in a different world than most where the expectation is we speak the truth, stand behind our word, and in the event of failure we maintain the relationship after resolving the conflict.
As for saving face, I provide opportunities to walk back, restate, or take back something that was said. People get angry, misspeak, or respond with fear and that is understandable.
In my house I do not permit "yeah", or "okay". It is "yes" and anything else is interpreted as a 'no'.
Once you press someone to speak a "yes" as a solid commitment, for example to an understanding of an instruction. If this puts the person on the defensive then you are dealing with someone who is not interested in being held accountable.
Let your yes be yes.