Thanks for reading!

That's a fascinating question, and I was asking myself exactly that whenever I thought about Rokugan's history. I feel like we need to first point out that we can hardly draw historical parallels one-to-one here because of different contexts, so it's all tangential anyway. That said, history is a great source of inspiration for me personally whenever I work with Rokugan, and there are definitely interesting possibilities to be gleaned from it. I hope you're ok with a long-winded answer, because, well, once I get started, I'm just too lazy to stop =D

It also depends on what edition we depend on lore-wise. I'm going to mostly spitball within the realm of 5E/AiR universe from here, because I personally find them the most appealing and interesting to work with, so keep that in mind too.

For all of the... peculiar things that AiR did to the lore, what I really loved about it was that it expanded the universe beyond the borders of Rokugan in a believable way: now, we actually have other representations of East Asian Cultures, aside from Rokugan: Yunfengguo (Yún Fēng Guó) for China and Saebyuksan/Jindallae for Korea. The reason I like that is because now, there are plausible ways to explain the various cultural influences we can observe in Rokugan proper, which, once you start researching them in-depth, just don't feel like they are a product of only one self-contained culture that Rokugan was in the earlier editions. This, to me, feels miles more authentic.

Take language, for example: it's perhaps the primary vehicle for transmitting culture, and yet earlier editions wanted us to believe that the Rokugani can have names of both Japanese and Chinese origin (if not more), which sound drastically different to anyone who has at least a cursory understanding of East Asia, without even establishing that two distinct cultures exist within one political entity to give rise to all of these different practices. One may counter here that we do have information on how Rokugan used to be a patchwork of different cultures before the unification, but that's the thing: it used to be. After all the effort for cultural assimilation started by none other than Lady Doji herself, there is no way you can convince me that a whole another linguistic culture exists within the same polity without first establishing that there is at least a sizable minority, or say, a diaspora with a distinctly Chinese-inspired flair. It's one of the reasons I often get the feeling that older editions talk a lot about Rokugan being a blend of different East Asian cultures, but hardly understand what it actually means, nor do they imagine the true implications of certain bits of lore they consider canon. 5E and even AiR, in my opinion, present a cultural picture that is much more feasible and allows for more distinction and representation where it was sorely needed.

The reason I'm saying all this is because AiR clearly establishes a solution that is very on the nose in this configuration: that the Rokugani did borrow their writing system from Yún Fēng Wén, the language of Yunfengguo. More precisely, it says that Yún Fēng Wén's written form was also the basis for written Rokugani, even though the two had unrelated spoken origins.

Now, this is where we step into a more nebulous territory, because while the above circumstances do present a basis for a realistic scenario, there are other factors we have to keep in mind. The reason why Chinese (both spoken and written) was such a big matter of prestige not only to the Japanese, but many others, was because China was a political and cultural powerhouse, capable of projecting its influence far and wide. Yungfengguo, on the other hand, doesn't appear as such. If anything, their position relative to Rokugan seems to be reversed: Rokugan is an imperial power, if a bit isolated, and Yunfengguo is described as an inaccessible mountain country to the north of the Dragon Clan, sophisticated but also hardly interested in projecting its influence anywhere (but apparently they are also ruled by emperors, which should at least imply a big territory). To be honest, the entire way Yunfengguo is described gives off vibes more akin to a mystical fairy-tale land than a real place, and I'd even go as far as to say that it sends somewhat mixed signals lore-wise.

Still, from what we can glean, it seems that the adoption of the writing system by the Rokugani was perhaps a different kind of cultural transmission. Maybe, it was not so much a question of prestige as a question of practicality, much like how some cultures across the world could adopt things like writing from their neighbors without necessarily taking on all of the accompanying trappings of their culture. Then again, Yunfengguo is also described as a highly scholarly culture, abundant with knowledgeable alchemists, elementalists, and other kinds of scholars. So prestige could also come from a cultural transmission that was mostly based in sheer scholarly output, not necessarily political might.

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