https://github.com/symfony/Translation/blob/decb41096e98a76e3759fdb042842b2f3838a6a1/Dumper/FileDumper.php

I really want to be able to send a file with Response object, but the format feature is protected and part of the logic to get to the string dump is baked into the file method.

I've resolved this in my code by hard-importing part of the components code and overriding the dump method and getting back the string (which is also kind of ugly and breaks the contract design), but it would be nice if there was a way to do this without writing a file.