The adverb of *unintelligible* — it describes the manner of speaking or writing, meaning it comes out in a way nobody can understand. It almost always sits next to a verb of speech: mumble unintelligibly, mutter unintelligibly, shout something unintelligibly, write unintelligibly. The grammar difference is worth being deliberate about. "His speech was unintelligible" describes the thing; "he spoke unintelligibly" describes the act. English writing, especially fiction, prefers the second when there is a person doing it — a character "muttered unintelligibly into his collar". It is a long, formal word and rare in speech; you will meet it far more in novels and reports than hear it at a dinner table. In conversation, people say "nobody could understand him" or "he was mumbling".

含糊不清地、令人聽不懂地