郷に入れば郷に従え

Excite翻訳: It is accompanied if entering the village in the village.
＠nifty翻訳: When in Rome, do as the Romans do
Babel Fish: If it enters into the home village, attending to the home village
Google翻訳: Place following the Township to Township
Yahoo!翻訳: Follow the volost if I enter the volost
OCN翻訳: When entering a village, follow a village.
Windows Live Translator: If entering the village to village accompanied

Summary:
@nifty has a fixed expression in its dictionary.
The others are trying direct translation, but omission of elements hampers correct translating.

Reverse Translation)
Excite翻訳: 村で村に入るなら、それは伴われます。
＠nifty翻訳: 郷に入っては郷に従え
Babel Fish: それが家の村に入れば、出席する家の村に
Google翻訳: 郷鎮に次の開催地
Yahoo!翻訳: 私が郷に入るならば、郷に続いてください
OCN翻訳: 村に入る時には、村に続いてください。
Windows Live Translator: 村々 にともなうに入る場合

Summary:
@nifty's is perfect.