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national language
Japanese language (esp. as a school subject in Japan)
one's native language; mother tongue
native Japanese words (as opposed to loanwords and Chinese-derived words)
国語の授業で作文を書いた。
I wrote a composition in language class.
国語の授業が一番好きだったな。
I liked Japanese class the most.
国語辞典で漢字の読み方を調べた。
I looked up kanji readings in a Japanese dictionary.