On a side note, why are areas separated based on countries of origin? If I were a muslim on the Hajj I'd be enthralled to be around people of all cultures and countries around me.
Its easier in terms of organisation and more easier to deal with groups of people who speak the same language rather than a hodgepodge. Many in these groups are illiterate and have never written or read in their lives, it can be quite difficult to manage people when one doesn't even speak their language.
Communication? It's easier to communicate to a crowd of people who speak the same language, if the need arises.