If prospecitive immigrants are not fluent in English or French already, it's perfect timing to study it while they wait to immigrate. Not just for an immigration interview but also to make it easier for themselves to get a job, go about daily life such as shopping, renting an apartment, getting a drivers license, buying a car etc. You can take English classes in most countries and it's good to use the time while waiting to immigrate to do this.
My workplace recentily hired a temporary worker who did not speak a word of English. They had been told he had basic English which apparently did not turn out to be true. They had no option but to tell the agency who brought him over to take him back since they can not use somebody they can not talk to. We felt a bit bad for him but since when did he know he was coming to Canada? Why was he not taking English lessons? So ok, most people on this board do at least have basic English but whatever your level is, if you can improve it all the better for you, easier to get a job, easier to do well in a job etc.