Nice list! May I ask what dictionaries do you use (I've just chosen from the internal list, but they seem not that "ideal" after Oxford)? By the way about backlight - on Android there is a bug with that feature: warm light can't be used and also if you start using automatic lighting it does not actually work. Not a big deal: just using system presets from device lighting menu.
I personally use a dictionary generated from a wikitionary dump. I used to use a script [1] to generate it, but some are now already available and linked in the KOReader wiki [2]. I found a wikitionary-based bilingual dictionary is quite good!
I use the ones from https://www.thefictionary.net for a few large series ( Cosmere, Realms of Elderlings, Malazan, Worm). Helpful to keep track of characters especially if you’re picking it up after a break.
I've bought a dictionary from Pons when that was still available many years ago, I dimly remember there was a script to convert it to StarDict. Nowadays it's a bit difficult because everything has moved to online services, you often cannot buy these anymore as offline versions. I'd suggest to go search mobileread.com and Reddit, there are usually good suggestions there...
