Mix the group to increase participation. Sharing experiences is one of the best aspects of international training. But don't count on participants to do it by themselves. Give the process a boost by mixing the group in various ways. Suppose you have 32 participants.
Some nationalities are naturally more outspoken than others.
Be sure everyone gets a chance to speak up by structuring the sequence of participation. Once everyone is in small groups, have the most senior member of group speak first, or the most junior. Ask the women to speak up first, or those who have traveled from farthest away. Acknowledge outspoken participants, but don't them overwhelm the conversation. I often do this by having small groups nominate a spokesperson, then having that person nominate someone else in the group.