I apologize that I read mistakingly as I commented.
Regarding your question-theory.
I have to start from the explanation about the history of the old ( not so largely discovered ) Japan in order to tell about Izumo Shrine.
There are many theories about the history of Japan up until around 6th century.
It is widely held Japanese ( or Japan ) was called 倭(Wa) which means barbarians ( to Chinese at that time ). Now according to the Vol 30 of Records of the Three Kingdom ( See the lower page ), which was written by 陳寿 ( Chen Shou ), around AD1-3, Japan seemed to have several countries centering around 邪馬台国 ( Yamataikoku ) Now, it is widely held at the same era, as I will mention later about Buddhism, Japan had had Izumo Shrine whose deity is and was Okuninushi no Okami, which has nothing to do with Buddhism. ( which indicates there might have been another different strong country against 邪馬台国 ( Yamataikoku ( which later became the main stream country which leads to today's emperor )))
Now, Buddhism, according to 日本書記 ( Nihon-Shoki ), which was written theoritically after the Yamataikoku conquered the main part of Japan ( Kyoto ), and was describing the old Japanese history and is written by traditional Chinese, from which Japanese later created its own Kanji and Hiragana ( = leading to today's language ), was imported to Japan in the year of AD538 by some historians ( or around that year by many historians ).
Today's Hiragana, oldest being officially confirmed in 古今和歌集 ( Kokin Wakashu ), although the development of Buddhism was almost in the same line with the spreading of Kanji and Hiragana, but it ( = Buddhism ) was imported from China and still practiced with Confucianism, the latter of which fitted with the idea and morality of old Samurais, whose main focus as the above Wiki says was the importance of the family, suited with Lord-subordinate system in feudal era at that time, and has been practiced until at least 1868 around that time Japan has begun trading with The United Kingdom, The U.S, Russia so on.
Another counter proof is the existence of priests of the Society of Jesus in 16th centuries in Japan, who traveled from Europe in order to spread Christianity and also for the purpose of trading. Japanese Christian, at that time was called 切支丹 ( Kirishitan ) who used Hiragana and Kanji to express their idea towards Christianity too, not Buddhism only.
So it is hard for me personally to relate the impermanence with the style of Japanese ( language ).
So do I believe personally about European alphabet.
And finally and most importantly you added Heidegger, even the Being is exsitable afte it is badged, then what exactly would you like to ask, sorry?
Simply saying, even the speech or text which comes after speech is the most important to human existence, are you proposing the style of the language differenciates what Foucault laughted out loud????????? I mean, the Western alphabets, which need the collection of the alphabets to denote something, differenciate the human Being itself because Asian Kanji is just a thingnification ( but not entirely, linguistically speaking ) such as 人, in English a person, expresssing the human being standing with two legs? and have you known before Buddha was born there had been a dynasties in China such as Chou empire and their characters?