I can comment the code a bit later if you want. I didn't think anyone would actually find it useful for anything more than seeing how simple it can be to implement both DTE and Substring.

And yeah, you can. I'm already with you: Toward the end of the day I started implementing the same routine in KGS1, and I noticed how little spare space there is at the end of the main code bank, certainly not enough to have a useful substring table. My solution is very much what you were thinking. It would actually be very simple to implement the substring table at the end of each code bank, and also that way each substring table could be even more relevant to that particular bank. It's possible though that it would take up more space than it saves. At the very least though, DTE usually already has table space allocated, so that shouldn't be a problem to implement.

The screenshots above don't show the DTE implemented, but it is now and works like a charm.

Pretty exciting times in the Gundam Knight Story translation scene. :p