There is no official "Directors Cut" English dub. If you find a file labeled "Oldboy English Audio," it is almost certainly the Tartan UK dub.
: Services such as the Sky Store and Apple TV often list multiple audio options, though availability varies by region. Distinguishing Between the 2003 Original and 2013 Remake Oldboy English Audio Track Download
Following the film’s massive international success, Universal Pictures acquired the rights for distribution in many territories. With the advent of 4K UHD and newer Blu-ray releases, the audio tracks were sometimes remastered or re-recorded to meet modern theatrical standards. Collectors often debate which English dub is superior, as voice acting direction can differ significantly between a niche distributor like Tartan and a major studio like Universal. There is no official "Directors Cut" English dub
But for English-speaking audiences, there has always been a debate: Distinguishing Between the 2003 Original and 2013 Remake