I tried this first, but found it really hard to recognize/remember [random-glyph] as "hello". Better if it's readable, even if unrelated, to make looking it up in the blab-o-dex easier. I may add a letter to separate conversations, so "H2" instead of "31". Still figuring it out.
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I'd consider trying it with short nonsense phrases written in the Standard Galactic Alphabet, of Keen and Minecraft fame. It was designed as a genuine font with the intention of players being able to legitimately read it, so it might work better, and it's already got a storied history of being used on mars.