is it cheaper to fly internationally on a friday or on a saturday?

Tuesdays are cheapest. Also wendsdays.

Fridays and Saturdays are usually more expensive....but rates change in December due to the holidays, so it might be less expensive to fly on Fri/Sat before the rates go up than on Tue/Wed after they go up. Check exact rates for particular dates just to make sure.

Tuesdays

And the time of the year also matters....

IE: Dates around "Holy Week" (in some countries) are much more expensive.

nope more expensive, week days usually is cheaper.. most cases

No. Its cheaper on tues /wed i believe