What is "critical messages" setting?
In "options" > "gameplay" > "basic" there's "critical messages" option (may be exclusive to the PC version). The game's tooltip explanation is non-existent "choose to show critical text messages in-game". Is the setting related to "critical" hits or something else?
No. Critical messages are those relating to the game objectives, such as "We have captured objective Alpha" or "The enemy has armed the MCOM."
By turing on this option, you will see the messages as text, not just hear them.