YOU SAID:
The cow decided to become friends with the horse
INTO JAPANESE
牛は馬と友達になることを決心した
BACK INTO ENGLISH
The cow decided to make friends with the horse
INTO JAPANESE
牛は馬と友達になることにしました
BACK INTO ENGLISH
Cow decides to make friends with horse
INTO JAPANESE
牛は馬と友達になることにしました
BACK INTO ENGLISH
Cow decides to make friends with horse
That didn't even make that much sense in English.