Japanese translations? Isn’t the entire original game in Japanese?
Indeed it is, however the remake has the texts from the English translation with adaptations and changes, which means that the remake has different texts to the original overall.
This means that there is 1 simple way to re-add the Japanese language which is to re-translate it to Japanese.
Alternatively one may take the original texts and re-fit them on the remake, but will have to do so with the nuance of adaptations and changes on the events and dialogue amount, leaving the original texts either in excess or lacking, which makes it a bit more difficult to add than just translating everything.