Fair Warning: this post is about 3.7 years old, so some of the information might be a bit dated. On the other hand, this post was last modified about 3.7 years ago, so maybe it's up-to-date after all. In any case, please keep all this in mind while reading. Thanks for understanding!
A Quick Diversion:

If you want an idea of which of the two Sinnoh-based games that people are more hyped about, all you need to do is just take a look at their video stats (which were accurate as of 2021/02/27 @21:29):

I think this proves what we all already know: that adults DON’T know why kids love the taste of Cinnamon Toast Crunch.

 

The Actual News:

I was about the kick off work on trying to figure out what the Sinnohese alphabet is, like gathering a list of characters and whatnot based on yesterday’s “Pokémon Presents” release trailer for both Pokémon Brilliant Diamond & Shining Pearl and Pokémon Legends: Arceus… but it looks like I was beaten to the punch! But that’s ok, it was a good beating. … wait that didn’t come out right

Anyways, PA! Discord user and Mug Root Beer afficiando, ElementsnStuff, posted some of his Sinnohese research over at the The Research Sector on the server. He even made a font for it; Hot diggidy’ dog! That said, if you don’t want to download the font, ElementsnStuff did at least post a picture of the Sinnohese text that has been spotted so far:

Now while some of these characters seem to be more “kanji-esque” more than anything, ElementsnStuff did notice some similarities between the Sinnohese characters and actual proper kanji. Specifically:

1 2 3 4 5 6 7 8 9 10 11 12 13 14
六 由 六 万 丁
大 方
穴

In fact, he also suspects that the 13th character in the list is used in the “snow sign” (right-most screenshot in the image above) in such a way that one the characters next to it is 地, and when put together it may mean 地方 chihō or ‘province’. I don’t quite see it myself, but my kanji is admittedly very weak, so you be the judge.

Another interesting coincidence which MAY also be meaningful is the fact that the book cover above uses five characters, and there are five characters in the Katakana transliterations of both “LEGENDS” (レジェンズ) and “ARCEUS” (アルセウス)… so maybe that could be a connection?

I’m a bit partial to it saying “ARCEUS” (アルセウス), as this makes more sense on a thematic level; afterall, it’s a story about Arceus… but then again, I could very easily see it be “LEGENDS” (レジェンズ), especially when you look at it this way:

But lol, this is just a total shot in the dark. (Please don’t actually shoot in the dark, it’s very dangerous!)

Anyways, that’s pretty much all I have to share. There really hasn’t been much to work off of anyways, and ElementsnStuff pretty much covered everything I would’ve done, so I really can’t say I have anything more to add. But when more news and research comes along, I’ll be sure to cover it here!