how do you say "Playlist"
播放列表 and 歌单 are both okay.

It's been translated as 播放列表 for long because of the early version of Microsoft Windows Media Player and other old players. You can tell that 播放列表 is directly translated because “play“ means 播放 and “list“ means 列表。

In 歌单， 单 is equal to 列表， and 歌 means the music that you wanna listen to. While in Chinese, 歌 mostly refers to the music with lyrics and that might be too narrow in meaning for there mignt be classical music without lyrics in your playlist. That's why I prefer 播放列表 to 歌单. The former has the more exact meaning.

Nowadays the people who listen to the music without lyrics are much less than people who listen to 歌， so 歌单 is also widely accepted and used by the public and sometimes replaces 播放列表. What's more, the word 歌单 is much shorter than 播放列表. I guess that also makes it more popular.