require with a voice to speak English or not?
or just use backsound be allowed ??
It is allowed even slideshow, if it will be interesting, informative and made in high quality. All limited by your own fantasy. Background English voice is not necessary condition and also it may be Spanish, Italian, German or Russian or other languages. You can use only video text, but of course videos with background voice will be rated higher.
that is simple and clear explanation to the deadline of the contest long enough,
hopefully this video contest running smoothly

I hope I can participate as a contestant of your video,
Can you escrow, to attract visitors interested in your video contest