You have to know they exist, and know when you should worry about them (and call in to the appropriate APIs)

https://manishearth.github.io/blog/2017/01/15/breaking-our-l... gives an overview of most of the different things scripts do. Being aware of those helps a lot. It also gives a brief idea of how to deal with this stuff (usually it's just calling an API)

https://manishearth.github.io/blog/2017/01/14/stop-ascribing... gives an idea of how grapheme clusters work. You don't need to know the algorithm, just the stuff around it.