English Translation
It’s not good manners speaking during the meal.
Current Clozemaster version: 食事中にもに{{ゃもにゃしゃべるのはお}}行儀悪い。
Correct word split: 食事中に{{もにゃもにゃ}}{{喋る}}のは{{お行儀}}悪い。(Note: I don’t fully support this translation, though.)
もにゃもにゃ is an onomatopoeia. It’s a sound of mumbling. But the English sentence doesn’t say so. So, もにゃもにゃ should be deleted from the sentence.
しゃべる should be spelled in Kanji 喋る. My alternative translation is:
食事中に喋るのは行儀が悪い。