Okay, first thing's first. How does it work?
Well, it's pretty basic really. It works by creating a box of Right-To-Left text embedded in a message.
.For the record, this is what RTL text looks like
According to Discord's RTL rules, the (edited) message appears on the left hand side of RTL text, and on the right hand side of LTR (normal English) text.
.(edited) That means it looks like this
So, by making a message (the contents can be ANYTHING), then editing it to contain a boxed message, Discord places our RTL text at the other side of the (edited) text. And we can still have "ordinary" left-to-right text in the same message.
Pretty cool, right?
I made this tool so you don't have to remember the RTL-embedding character. (It's U+202B.) Note that it's a non breaking character, so it behaves a little weirdly if you try to type it out manually.