Generally representing dialog is not a problem. In the case that they want to represent a word/sound that does not have a character assigned to it there are a n

Generally representing dialog is not a problem. In the case that they want to represent a word/sound that does not have a character assigned to it there are a number of strategies to deal with it: romanization (pinyin), zhuyin fuhao (phonetic notation), non-standard character or pick a character with similar meaning or sound. Generally context is sufficient for native speakers to figure out what they are trying to convey.