I think what you consider the hardest part, putting it together so that someone who does not speak any human language today deciphers it, is actually one of the least of your problems. Unless you deliberately encrypt the information (which you wouldn’t), I have a feeling that even Wikipedia alone might be sufficient for a motivated civilization to figure it out. Linguists and archeologists in our time have to do with far, far less, and they have reasonable success. Add in a few things like dictionaries, textbook, novels, and I have little doubt that it’s a big obstacle.

Rather I think you vastly underestimate what a billion years can do. The earth itself, and all that was on it, was formed a “few” billion years ago.

Our rivers alone have carved entire valleys into mountain ranges in much, much less time. I doubt a titanium alloy and some unspecified sort of super epoxy stand a chance.

And constant custody with regular restoration cannot be guaranteed for billions of years either.

That’s a massive problem for one plate (and its many copies) alone, more so for millions of unique plates…

The Long Now Foundation is only shooting for 10000 years, as far as I know.