YOU SAID:
my dog is my cat's dog's girlfriend
INTO JAPANESE
私の犬は私の猫の犬のガールフレンドです
BACK INTO ENGLISH
My dog is my cat dog girlfriend
INTO JAPANESE
私の犬は私の猫犬のガールフレンドです
BACK INTO ENGLISH
My dog is my cat dog girlfriend
That didn't even make that much sense in English.