Pretty sure there is currently no way to mod this. I found the messages around line 8920 in game.cpp; it will always print the messages if it detects that the player is “slowed”, which happens any time they move on to or off of terrain that has an increased movement cost. I’m sure there are ways that these messages could be made optional, but I don’t know if anybody actually wants to modify the code to do it. I agree that these messages are essentially just spam after a while, especially in situations like walking across an open field where every other tile is long grass.
