Your audience speaks English, Spanish, and Mandarin; your keynoter speaks English. Time to call a translator, right? Wrong. Translation involves the written word. If you want your non-English-speaking guests to understand the key-note, you need an interpreter.
Actually, unless the keynote is less than a half-hour long, you need two interpreters. Because of the intense concentration required for simultaneous interpretation, interpreters work in pairs, alternating every 20 to 30 minutes. Good ones don't come cheap: Look for them to charge between $500 and $900 a day, depending on the language, the local supply of interpreters, and other factors.
You'll find this information and a whole lot more packed into the airline-ticket-sized Meeting Planner's Guide to Simultaneous Interpretation, published by MFM Simultaneous Interpretation, based in Miami.
Among the other things you need to consider: allocating enough space for the interpreters' booths, deciding whether or not you need floor microphones (will there be audience questions?), and providing interpreters with acronyms and terms relevant to your industry before the presentation.
To get a free copy of the guide, which also includes cost-saving tips, call (800) 814-6548.