口語 - 我已經回到家了

口語的話全都不對

因為係講自己回到了家...而不是描述講述一個叫自己的他人回到家
所以從你自己講話的角度雖然你想指出你是「已經」，但是現實處境狀況是「你在家了」。

所以你的講法(亦是英語人的講法)應該是

I am home already.
是用現在式的

假如你仍想問必須要用perfect tense作句來講述你已經回到家，例如向另一個人報告...
則應該用arrive，而不是用不是動詞的back...，
I have just arrived at home.
I have arrived home.

back只會在配合動詞的處境，例如go back: I have gone back home by myself.
講這話是事後講述番而不是現在通知你，立場不同便要用不同的動詞。

(1)但是應該是I have already gone home?

口語 - 我已經回到家了

I got home already.

Just simply say "I am home."

坐飛機,剛返家,去電給媽媽, 免掛念
簡單口語, "Mom, I'm home."
或長少少 - "Mom, I've just returned home."
return = 返回

arrive at home ~ at 是多餘, 是初學者講
除了 arrive at your new home (your new home 是 noun phrase)

通常講 arrive home,
home 是做 adverb
arrive/get/go/reach/return + home

2013-10-24 02:02:08 補充：
Instead of using the word "retutn", you can say
"Mom, I've just come back home."

(1)back=adv.=return;
been back already=return into the place or position where someone was before=home.I was supposed to be back at home by 5pm.Now you found me home at 5 pm.
been back home=better go back home.
(2)have back=present perfect tense=again=once again
eg:-Let us go back home just to make sure we're back home.