How to say good luck in Japan

Pretty well as the title says a friend of mine is going to Japan for three months on Thursday, and I just wanted to wish him good luck In Japan, but I wanted to do in japanese :)

help will be great

THank you all you helpfull people of Japan guide :)

Don't know of an equivalent, but you can say:

Yoi Tabi O

which means have a good trip

"genki de ne!" = Be well!

I think your friend will understand Japanese quite well, since you want to say it in Japanese. Therefore I would recommend somewhat classic and formal phrase:

道中のご無事をお祈りしています。
あなたの旅が実り多いものになりますように。

Dou-chuu no gobuji wo oinori site imasu.
(I pray for your safety during your travel).

Anata no tabi ga minori ooi mono ni narimasu youni.
(May your travel be very fruitful.)

日本での幸運を祈っています。

nihon deno kouun wo inotte imasu.

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Literally translated.

personally i cannot imagine a young person ever using "inoru" to their friend going on a trip, nor can i imagine young people using desu/masu to their friend

IMO something like 楽しんできて！ / tanoshindekite! would be more common / normal among young people.

be sure to check out how to pronounce japanese properly before trying to speak it or your friend probably won't understand what you're saying. fortunately japanese pronunciation is REALLY easy to learn.