YOU SAID:
My dogs been sleeping for 8 days.
INTO JAPANESE
私の犬は8日間寝ました。
BACK INTO ENGLISH
My dog slept eight days.
INTO JAPANESE
私の犬は8日間眠った。
BACK INTO ENGLISH
My dog slept for 8 days.
INTO JAPANESE
私の犬は8日間寝ました。
BACK INTO ENGLISH
My dog slept eight days.
INTO JAPANESE
私の犬は8日間眠った。
BACK INTO ENGLISH
My dog slept for 8 days.
it is unlikely that this phrase will ever reach equilibrium