To be technical for a moment, an STBL file uses a . The key is a unique hash (a fixed-length string generated from the original text), and the value is the actual localized text that appears in-game. When you edit a string, you are changing the value attached to that specific key.
When EA releases a patch for The Sims 4 , updated string files are placed in the Delta folder rather than overwriting original Full installation files. This design choice means: