When editing the Instance ID of a String Table, the first two digits dictate the language: 00 : English 01 : Traditional Chinese 02 : Simplified Chinese 03 : French 04 : German 05 : Italian 06 : Japanese 07 : Korean 08 : Dutch 09 : Norwegian 0A : Polish 0B : Portuguese (Brazil) 0C : Russian 0D : Spanish 0E : Swedish 0F : Finnish 10 : Danish 11 : Czech Best Practices for Modders and Translators
If you are building Python scripts, you must learn how to inject strings via the _strings.txt resource. sims 4 language strings best