Working with a Japanese conversation partner, I am currently translating a Japanese short story in which a young couple, Koichi and Sayo, go to her parents' house in Nagoya for the August bon festival. This Buddhist-Confucian custom has evolved into a family reunion holiday during which people return to ancestral family places and visit and clean their ancestors' graves, and when the spirits of ancestors are supposed to revisit the household altars. (Thank you, Wikipedia.)
The couple met in Tokyo working for the same company, married in March, and while their relatives came up to Tokyo for the wedding, this is the first time Koichi has spent any time with Sayo's parents, a more formal, traditional couple than Koichi's. Koichi and his father-in-law have virtually nothing to talk about and Nagoya in August is too hot for a walk around the neighborhood.
After a huge dinner and strained conversation, Sayo suggests that Koichi be the first to take his bath. (In Japan, one washes and rinses oneself thoroughly before entering the bath tub, which means everyone soaks in the same bath water.) Koichi, respectfully, says he should not go first. His father-in-law, the most senior person in the family, should go first.
The father-in-law says, 「ぼくはいつも寝る前だで」 Or, "Boku wa itsumo neru mae da de." Or: "I always go before sleeping."
Sayo says from the next room,「ぼく、だって」Or: "Boku, datte." Which more than I could translate and once again needed the help of my Japanese conversation partner.
Boku is one of several words in Japanese that can be translated "I." Others include watakusi, watashi, atashi, ore, shôsei. Datte can be translated "because," "for," "but," or "though."
For the daughter to say to her father, "I, because"(or one of the other alternatives) doesn't make any sense.
My partner explained that in this situation, the daughter was asking her father why he used a formal form of "I." Does English even have an informal or formal form of the personal pronoun?
So, an acceptable translation might be, "Dad, why so formal?" Which, of course, uses none of the original Japanese.