Why would you ever want to train askari over bowmen as the Africans? Bowmen have an amazing rate of fire, deal quite a bit of damage for a skirmisher, more than the askari, and have insane range in the later ages. They're dirt cheap too. The only negative is that they are really squishy (but then, so are the askari) and that they cost wood instead of coin, the former of which starts to run out in the late game. Even Ethiopian askari are worse than their bowman
In the scenario editor, a bowman beats an askari 1 on 1 even if the askari fires the first shot
In addition, the only civ I would say has reason to train askaris is the Italians, of all things- they get a card which lets their explorer train askaris in the second age, which are a lot less squishy than their ordinary infantry.