The text can be legible, but the meaning the model assigns to these words can be subtly different, and you have no way to tell. This is evident when trying to make most modern reasoning models follow a fixed CoT plan by filling a form with placeholders, they're extremely stubborn because they simply don't understand your words in it! They learned their own language in their CoT. Sometimes they're controlled for readability during training but even then they find a way to circumvent this, for example Gemini 3.0 had perfectly readable raw CoT but was barely able to follow such a plan (3.5 Flash is way better at following, they clearly improved it).