All of the PC's speak Common -- which for our purposes, as you are all in the Aquilonian army, means the language of Aquilonia. If you're not from Aquilonia, you have an accent, but you are all fluent enough to get by. You also speak your native tongue -- from whatever land you hail from. These are at no cost and part of the base build.
For characters with higher INT scores, the option for more languages is possible. You might consider learning Turanian -- you are in Turan and have been for weeks at least. It is the language the bandits spoke and will be useful.
In considering languages and home lands, this link will be useful:
https://hyboria.xoth.net/races/human_races.htm
Until you tell me you have learned it, you will not understand the locals, only the Aquilonian speakers -- army command, traders, etc.