Square-Enix hasn’t talked much about Final Fantasy” The Four Warriors of Light in either North America and Europe. According to Siliconera the title is heading outiside of Japan with the current name of Final Fantasy: The 4 Heroes of Light.
Why is this marked as a rumor? Siliconera doesn’t provide any sort of source. I think Siliconera is a pretty respectable, so I’d say it is likely that it is. But I’m playing it safe with a rumor mark.