If you need some examples of characters who speak in a Ye Olde English accent, I can think of Cyan (FF6) and Frog (Chrono Trigger) off the top of my head. The accent alone doesn't make them great characters, but it certainly adds to the flavor.
Fiora already speaks in a French accent, so why is there no Ye Olde English?
Guessing: either they haven't thought of a reason to do it or
that having a character speak Middle English would be a ton of work to do correctly and would make some people's ears bleed if they didn't.
...It's bad enough people pronounce "Ye" with a "y" sound as it is.
That's more of a dialect than an accent, and there's no reason for a character to speak a new language unless they have a community with which to speak it.
Hmm, I dunno. Tahm Kench speaks with a caijun accent and has apparently 100 quotes for various other champions (both enemy and allied)
