Science Fiction novel - young human does not want to fight, instead investigates crimes with alien who communicates with smells

[Jacob]

I read this book between 2005 and 2010, but the feel makes me think it was written before 2000.

SPOILER? - General plot not the ending:

A human lives on a planet populated by many species. The humans have a fighting centered society - when you turn 18 you fight in an arena, the strong who win are allowed to reproduce and have children, but if you are weak and lose you are neutered and can't have kids.

Main character is about to lose and not be able to have children - I believe he just doesn't want to fight but he also might be bad at fighting. He befriends an alien who communicates through smells / scents. Since there are so many species there are universal translators but only from one language at a time - if you want to switch the language you are translating you switch which translator you are using. This alien species emits smells to communicate, which can be picked up and translated.

The main character helps this smell alien investigate some crimes and learns a lot about himself and figures out his future or something of the like. Its very much a coming of age mixed with investigative mystery.

Feels like an older style book, similar to Jhereg for example, based on the descriptions of technology and setting chosen.

Thank you for reading.