Hello, i was thinking on a bug on this achievement, and i was writting a topic on the Tech Support section, then, when i've gone to look for the translation fr -> en of this achievement, the answer come to me.

The achievement wasn't bug, but just wrongly translated.

English ->

By Any Means

Complete your control of an ocean by trading for a Fortress.

Trading -> Business or commercial exchange/selling

French ->

Par tous les moyens

Finalisez votre contrôle d'un océan en acquérant une forteresse.

So, "Acquérant" is a conjugation for Acquérir, and is translate to Acquire (seems obvious) and this is mostly use for a hard or brutal way of taking things.

Completly opposite to business.