Why are there different audio levels for different languages?

I have not seen the trailers you mention, nor have I ever made a trailer, but this is my guess:

By necessity, trailers are completed before post-production is completed. Thus, the final audio mix is not complete. There is no baseline source (thus volumes), for say, a scream, relative to background noise. In fact, the actual scream from the movie probably isn’t even captured. And even if it is, it might not make the final cut. As I understand it, a production company will outsource languages to different agencies. Savvy US producers do not presume they understand intimately the UK and other markets as well as local specialists do in a right-this-second kind of way. Trailers are often outsourced to these specialists who do their own thing even though it’s the same language (some might argue that.)

There are standards, but no integration after the fact of the different trailer products, or direct communication during their creation where various artistic decisions are being made in parallel. There is no reason to level-set them after the fact volume wise. These trailer artists are all about bang-pow, and could not give a hoot about trailer consistency between countries. (Unless technology, allowing direct head-to-head comparison, and inquisitive people like you, start to generate a problem of it.)

Also, if I took Led Zeppelin’s first album, and recorded it to cassette on my system (wow – that’s dating me), and my brother did the same on his system, and my sister on her system – even though we had the exact same recorded source (even though trailer companies do not), our cassettes would probably sound very different played head-to-head, because of the probability of different cassette manufacturers with different tape biases, and our chosen noise reduction schemes, and equipment.

However - you can pay to have it all made consistent, if you have the inkling, money, and time. This is one of countless artistic decisions made in move creation. It is an insane thing they do, making the magic! Much respect.

When different movie languages are being mastered to a single DVD, you can be sure there will be more consistency. These days, that is. Not so in the past.

This is just a humble and imaginative SWAG at your question. I’ve never opened the proverbial clock to see how it works, that’s just how I imagine it might work, in at least one imaginative case. I would love for the trailer creators to give the real story.

(No technicians were harmed in the making of this production.)