"II" is hardcoded in the tooltip of the beacon effect button for upgrading the effects to level II. This is inconsistent with other parts of the UI, and makes it so that resource packs cannot change the string. It should use potion.potency.1 translation string instead.

Found while mapping GUI for Fabric.

Code from BeaconScreen's inner class (Mojang mappings, 1.18):

...
@Override
protected MutableComponent createEffectDescription(MobEffect effect) {
        return new TranslatableComponent(effect.getDescriptionId()).append(" II");
}
...

It should append a space and new TranslatableComponent("potion.potency.1"), not (" II").