https://jref.com/society/trivia_japan.shtml
The old Japanese language was a blend of ancient Korean and Ainu language. Since the 6th century, Chinese characters (and the words that go with them) were imported into the language, and now amount to about half of the vocabulary in Japanese.
i think it is completly wrong because there is no document

70% of korean language Pronunciation of word
are chinese. There is hardly commonness of Japanese and a Korean language in syllable or 語韻.
anyway there is no document of korean sound at that time.
Btw. last night, a korean said " there is no 概念(concept) in Japan
then I asked what concept...........
anyway I could not understand at all until last.
then a Japanese told me " 概念" in korean means "common sense".
what?
so I understood they dont know the meaning of origin because of hangul.
I do not think that there is superiority or inferiority in the language..................

it is said Japanese language is mysterious though there are many document.
in General ,it is said Kanji transmitted from China was 7th CE.
However, there is some traces where the japanese were using Kanji from B.C.
When Japanese was not able to be described by the letter , number of Japanese phonemes seems to have been more than that of now like ゑ ゐ.
It is possible to avoid misunderstanding now if it writes by the character even
because of a vague pronunciation.
However, I think because it was necessary to listen to the word because of the sound in the age without the letter, a vague pronunciation might not have been permitted.
In the civilization without the character, the race's memory was told by oral tradition
Ainu language - Wikipedia
ainu has more
as for freely expressed , the Japanese who had taken the Chinese character into Japanese did various devices.
The phoneme that cannot be expressed by the character might be weeded out, and it been fused with the phoneme of the approximation.
as for Korean language, it was as mysterious as Japanese.
Korean did not have an original character, and did not esteem an own language culture.
Korea was disregarding not only the language culture but also the home country culture.
In addition, even the scholar at the level by which the country is represented gets beaten up if he or she puts out research results to disobey race's feelings now.
Therefore, the research of Korean language by the Korean people seems not to advance easily.
There is no material even if they wants to research.
surely, it become it mysterious....
I think that there are considerably a lot of phonemes of a Korean language
compared with Japanese.
and they are poud of that.
that is why The Korean seems to understand Korean is superior language.
indeed, the number of phonemes in korean decreases obviously
I think that it can be an advancement that the phoneme is weeded out in a certain language in the phoneme linguistics.
However, on the other hand, room where the misunderstanding is caused when communicating by the pronunciation comes to increase.
In Japanese, the room for the misunderstanding has been buried by using the Chinese character.
as far as Chinese character is used even if the phoneme is few and the pronunciation is changed , the meaning can be faultlessly told.
They cannot search what meaning former word has from the character.
Therefore, even if they use the character, they are searching for the meaning of the word because of the sound that not the character but the character shows.
that is why they fall into strange peculiar ideas by Hangul only of
the pronunciation.??