Why were the Japanese screaming all the time?

Its not real life… right?

Yelling is kind of a Japanese cultural thing. If you're in command, you always yell constantly.

It's also just a movie.

Maybe they saw... Godzilla?

I didn't really notice it. I just thought it was the way they spoke, seems to be the way in many films with Japanese people from memory. Some cultures speak louder in general than others. I live in a very multicultural region and it is interesting (and sometimes funny) the way some people talk so loudly during normal conversation.