Translation of driver’s id

I lived in Japan for a year in 2015, arrived January 2015.

I got a translation of my driver's ID (I'm German) in July 2015 and used it to rent and drive a car in August 2015.

I returned to Germany in January 2016 but will travel Japan in October this year.

Do I need to get another translation of my driver's ID? (I looked at the JAF but it confused me)

Thank you in advance.

As the lady told us when we got our IDLs, it is valid up to one year from the issue date, so I think you'd need to get another one.

OP is not asking about IDLs but about Japanese translation of his German driver license. They are needed for the handful of countries whose IDLs are not valid in Japan.

http://www.jaf.or.jp/inter/translation/specific.htm
翻訳文の有効期限は免許証の有効期限と同一です
but, the validity of translation does not mean straightly your license validity in Japan. there is another restriction. you have to leave Japan in more than 3 month term, to reset the validity of one year.
(in OP's case, he/she left Japan in Jan. 2016 and return to Japan in Oct. 2016. it shows a leave of 9 months long and the validity will be reset.)

Dated translations don't seem to be specifically required so it is likely still valid as long as the particulars of the translation haven't changed. Better contact the embassy to be sure.

That's what an IDL is: merely a translation of your home country's license in an array of languages.

Maybe it's different in Germany?

It is different in Germany as they are not party to the 1949 Geneva Convention. Instead one only needs a simple translation to drive with a German license. More info here:

http://www.japan-guide.com/e/e2022.html