Demon's Souls: I test against the US version, but any valid full game dump of Demon's Souls will probably work out of the box.
This, of course, only applies to the PC version of Dark Souls. Dark Souls 3 and Sekiro: Use UXM to extract the game files.
The UI III mod from Khonziel may not represent a dramatic change, but it cleans things up a bit, sharpening the resolution on some images, and it has been well-received by users. Give Dark Souls a Dark Souls 3 UI makeover with this mod If you want to revisit Dark Souls but prefer the third game's user interface, this mod has you covered.