YOU SAID:
today is my favourite day because it`s my bihrtday!
INTO JAPANESE
今日は私の誕生日なので、私のお気に入りの日です!
BACK INTO ENGLISH
Today is my birthday, so it's my favorite day!
INTO JAPANESE
今日は私の誕生日なので、私の大好きな日です!
BACK INTO ENGLISH
Today is my birthday, so it's my favorite day!
That didn't even make that much sense in English.