Language difficulties always happen to non-native speakers. Moreover, not all people can speak English well. Let's say, in one situation where an old lady comes to you asking about something, and a language difficulty arises.
Old lady: 你好..!@#$%^& (in Chinese language and you understand only 你好)
*你好 (ni hao | ㄋㄧˇ ㄏㄠˇ) = is used as a greeting, can also mean "How are you?"
To reply 你好 (ni hao | ㄋㄧˇ ㄏㄠˇ) is 你好 (ni hao | ㄋㄧˇ ㄏㄠˇ) itself.
Here are some other replies that can be used:
*You can add Sorry = 對不起 (dui bu qi | ㄉㄨㄟˋ ㄅㄨˋ ㄑㄧˇ) in front of the sentence if necessary.
Can you speak English? = 你會說英文嗎? (ni hui shuo yingwen ma? | ㄋㄧˇ ㄏㄨㄟˋ ㄕㄨㄛ 一ㄥ ㄨㄣˊ ㄇㄚ?)
*English = 英文 (yingwen | 一ㄥ ㄨㄣˊ)
I don't understand Chinese = 我不懂中文 (wo bu dong zhongwen | ㄨㄛˇ ㄅㄨˋ ㄉㄨㄥˇ ㄓㄨㄥ ㄨㄣˊ)
*Chinese = 中文 (zhongwen | ㄓㄨㄥ ㄨㄣˊ)
I don't understand = 我不懂 (wo bu dong | ㄨㄛˇ ㄅㄨˋ ㄉㄨㄥˇ)
*不 (bu | ㄅㄨˋ) = no (negative)
*懂 (dong | ㄉㄨㄥˇ) = to understand
Can you write it down for me? = 可以寫給我嗎? (keyi xie gei wo ma? | ㄎㄜˇ ㄧˇ ㄒㄧㄝˇ ㄍㄟˇ ㄨㄛˇ ㄇㄚ?)
*write = 寫 (xie | ㄒㄧㄝˇ)
Can you say it one more time? = 可以再說一次嗎? (keyi zai shuo yici ma? | ㄎㄜˇ ㄧˇ ㄗㄞˋ ㄕㄨㄛ 一 ㄘˋ ㄇㄚ?)
*說 (shuo | ㄕㄨㄛ) = to say, to speak
*one more time = 再一次 (zai yi ci | ㄗㄞˋ 一 ㄘˋ)