String-tables (stringtable.csv) are methods of storing multi-lingual text outside of your code. They have absolutely nothing to do with the display of text, though string-table text can be shown on the screen. Are you perhaps trying to use something like:
titleText (localize "STR_MY_STRING");
In which case you are asking a question about titleText (or whatever other command you are using to display the text), not about string-tables per se.
One issue with string-tables that might be causing you problems, though, is that string-tables are only updated when you save the mission, not when you run it. Thus, if you have added string-table entries and not saved the mission before you run it again, the strings would not be recognised and would just be displayed as "" (or nothing on the screen).