YOU SAID:
Lost in translation, indeed
INTO JAPANESE
訳がわからなくなった
BACK INTO ENGLISH
I got forgotten.
INTO JAPANESE
忘れてしまいました。
BACK INTO ENGLISH
I have forgotten.
INTO JAPANESE
私は忘れてしまいました。
BACK INTO ENGLISH
I have forgotten.
That didn't even make that much sense in English.