Overriding day of the week strings in game and calendar

Hi! I'm looking for a file or at least a specific package in base TS4 game to translate days of the week (Monday, Tuesday...). I've found the strings in the base game which correspond to the work days (M, T, W...), and span class with list of uncapitalised days but it doesn't seem to change anything in-game when I change the string. 

I suppose this file is hidden somewhere in the packages in Delta directory. Maybe, some of you may know where can I find these. Thanks!