Formal shirts- sleeve length.

In India, foraml shirts are both full sleeved and half-sleeved, like a bush shirt. The temperature in Japan in August would be 30 degree C. A half sleeved shirt would be comfortable. However if it customary to wear only full sleeved shirts, then cotton ones would be fine. Information required to pack my luggage.

Today it was 35 degrees! What situations are you planning to wear your shirts in? If it's for casual wear, than wear whatever you like. For work, it can depend on the company, but with the introduction of "Cool Biz" a few years ago, short sleeves are becoming more common.

I do notice that a lot of salesmen still need to wear suits.

That said, as mentioned, "Cool Biz" that the whole government is advertising is a good excuse for everyone to wear short sleaves and no tie with your top button opened.

Even the best department stores make constant announcements so that no customer can complain about their short-sleaved costumes.

If you're concerned about wearing short sleaves, just make sure you tell every person you meet that you're following "Cool Biz". You'll be helping to keep a CO2 reduced environment.