It depends very much on their level. However, if the problem is one of confidence, then this is a separate issue. Many fear speaking because they worry about making mistakes and somehow seeming 'stupid' when talking to native speakers. However, if this is international, then there will be many other nationalities in the same position. Very often, all they need is somethig to break the ice and make them realise that they are capable of communicating and that this is the essential. Can you get a native speaker in to one of your meetings? If so, then bring them in, without warning, and force them to say a bit- once they've started, they'll find it easier.