The English language is used throughout the world, however when you have conference call attendees that consider English their second language and live in places such as China and Poland there are some factors you might want to consider in order for all the participants to fully grasp your comments:
Americans are known as fast talkers. Slow down your speech so the "English as a second language" folks won't get frustrated or misunderstand your agenda.
Don't sprinkle your speech with metaphors or jargon. International attendees might be puzzled by your comments. If you say "Cat out of the bag," they may find it difficult to understand why you put a cat in a bag.
At appropriate times, ask the international audience members if they understand your comments and if they have any questions.
Sometimes it might be appropriate to hire an interpreter to assist you during the event.
Be careful with using humor in your speech. You may end up saying something offensive to English as a second language participants or saying something that makes you seem ridiculous and they loose respect for you.
Be on time. In some countries being just a few minutes late is an insult.
Your etiquette may have to be adjusted when working with an international audience.