As a general comment, another avenue to investigate when trying to figure out what's going on with something that's stumping you is to take a look at what other people have already done. For a text-related issue like this, you might want to take a look at some translation patches, and as it happens there are one
on this site that even have screenshots showing modifications to the treasures screen.
As for the actual text, I think you'll find that the format is pretty simple: for each string, there's 1 byte to specify the screen X co-ordinate to start writing text to, then the text to write, terminated by $FF. If you make the text longer, you'll want to start writing at an earlier tile (smaller X co-ordinate) or use up some of the spaces between columns. As usual, if you change the lengths of any of the strings, you'll also have to update their pointer table, which you can find starting at $94AD.