My setup: Linux Mint 17.3 + Italian keyboard. In this keyboard layout, '~' (tilde) and '`' (grave) are not present, '^' (caret) is present, but is a shifted character. In short, none of them can be used to open the console. I tried switching to the English US keyboard layout and they do work as advertised.
However, it is rather inconvenient having to set multiple keyboards up and to switch from one to another in order to access the console.
I hope something can be done to improve the matter.
Thanks,
M.
P.S.: I tested only the single player mode, but I assume it is the same in multi-player mode.