Try to keep it practical (like something that would be fairly doable, you just havent gotten around to it…yet)
There are apps that you can input text into and they can replace the characters in each word incrementally to help learn them. Wanna get into that
The general knowledge of prefixes, suffixes and sentence structure of the language families/subgroups, in order to better grasp a basic understanding of a common language when I encounter it, and be more respective - for example knowing when to use -kun, Fraulein, señora, and courteous actions native to the locale