関連ワード:  how many words to be fluent in japanese    how many words to be fluent in a language    how many words to be fluent in spanish    how many words to be fluent in english    how many words to be fluent    how many words to be fluent in french    how many words to be fluent in german    how many words to be fluent in chinese    how many words to be fluent in korean    how many words to be fluent in italian