Quentin Tarantino has worked with English actors like Tim Roth on several occasions. Still, the filmmaker felt he had a solid ear for accents, and could tell when non-American actors sounded off. This would later affect the way he worked with Roth and other non-American performers.
Quentin Tarantino felt non-American actors lost their charm without their natural accents

Tarantino and Roth started collaborating under unique circumstances. The filmmaker famously cast Roth as the Reservoir Dogs character Mr. Orange, but only after a night out of heavy drinking. When a much more sober Tarantino realized what he’d done, he soon thought he made a grave mistake.
This was Tarantino’s core reason for letting Roth speak in his true tone.
Tim Roth was angry that Quentin Tarantino almost shelved ‘The Hateful Eight’
Roth was sure it wasn’t a bluff on Tarantino’s part, either.
“He probably thought, ‘Oh this is good. I can do this,’” Roth said.