Hi there!
“Perhaps the Editor team could make the key used to open the console rebind-able by the users”
Have either of you tried going into your project’s Config/DefaultInput.ini
and adding these lines?
[/Script/Engine.Console]
;change this to a different EKey name
ConsoleKey=Tilde
TypeKey=Tab
I’m not sure how the Key naming scheme changes for Japanese keyboards, but I have a list of all possible values in the Keys Enum on my tutorial page.
http://forums.epicgames.com/threads/972861-TUTORIALS-C-for-UE4-gt-gt-New-Complete-Code-Custom-Screenshot-Save-System-For-You?p=31660286&viewfull=1#post31660286
I’d put the whole thing here, but it’s reallly long 
you can try playing with changing ConsoleKey to any of the values below/in my tutorial
Again I’m not sure if the Enum struct is different in Japanese version, but this struct is in InputCoreTypes.h if you want to check
here’s the first part of it:
UENUM()
namespace EKeys
{
enum Type
{
MouseX=0,
MouseY,
MouseScrollUp,
MouseScrollDown,
//slate uses Spin
MouseWheelSpin,
LeftMouseButton,
RightMouseButton,
MiddleMouseButton,
ThumbMouseButton,
ThumbMouseButton2,
BackSpace,
Tab,
Enter,
Pause,
CapsLock,
Escape,
SpaceBar,
PageUp,
PageDown,
End,
Home,
Left,
Up,
Right,
Down,
Insert,
Delete,
Zero,
One,
Two,
Three,
Four,
Five,
Six,
Seven,
Eight,
Nine,
A,
B,
C,
//....
//some other exciting candidates :)
Semicolon,
Equals,
Comma,
Underscore,
Period,
Slash,
Tilde,
LeftBracket,
Backslash,
RightBracket,
Quote,