For events without interpreting:
All languages are important. While English is the dominant language in the US, there are lots of people in the US whose first language, and the language spoken at home, is other than English. Please raise your hand if English is not your native language (You might ask them which languages they speak) We will attempt to speak slowly so that everyone can understand. Please let us know if we speed up and need to go slower.
Useful information for leaders: Slowing down, using clear and simple language, and avoiding the use of US-centered expressions and colloquialisms are all useful for non-native English speakers. If there are two folks with the same language, you could encourage them to do the listening exchange together.