I've only played the one Yakuza game, but I know in later games they have English dubs, and I'm like "Doesn't that defeat the point of them being Japanese?", it's for moments like this that it would make sense.
If Infinite Wealth will have english dubbing then what will those beach-goers sound like?
Actually only the original Yakuza 1 on PS2 has an english dub (and also Fist of the North Star and Judgment if they are counted).
Infinite Wealth (trailer) is happened in America so it makes sense if they are talking in English
(though probably it's just to show that Ichiban was not in Japan again and the language could change into Japanese again when the game started)