The question is: how transparency is being implemented in modern games?
In the way that best matches the graphical needs of the game. Yes, this is a broad answer, but the situation hasn't changed a lot over the past 15 years.
Most 3D games will still do the usual 2 rendering passes:
- Opaque pass where all solid objects are drawn sorted by texture/shader first, near to far second
- Transparent pass where all translucent objects are drawn strictly sorted far to near.
Sorting by distance is cheap, Quicksort and Mergesort are highly efficient. But what really sucks performance is the need to draw strictly far to near in the transparent pass, since this breaks any texture/shader sorting. And switching textures and/or shaders creates a very noticeable performance hit.