It's so weird because of how involuntary it is. I notice that on signs in languages I can sound out, my gaze will stick on the sign until I can "read" it, without me wanting it to happen.
The first few days in a new country can be kind of exhausting simply because of this effect.
Like many Indians, I was raised bilingual on completely different scripts (Latin alphabet and Malayalam) and learned the Hindi (Sanskrit) script when I was really young too. I learned to read Hangul in the first 2-3 days of wandering the streets of Seoul aimlessly when I stayed there for a month, just trying to read every neon sign, advert and train/bus stop I came across.
The thread works at slightly different paces for each of them because of how much I use each one, really feeling like it's all about cache hits and memory bus limitations. It's pretty interesting to meta-think about.