The best way to converse with clients who do not speak English well, is to adjust your speech level to theirs. This is something that could be termed as an efficient way of communication. There are several different practices that one can adopt in order to make communication between two parties more effective.
For instance, one could also try and speak slowly so that the client could understand the entire message word to word. Similarly, it would be better to adjust your accent according to theirs so that they can easily follow each and every word, and can interpret your message the way it is.