How can I change LANG?

When I assigned command+c to btt for coping some text in clipboard, the text encoding would be shift-jis.
The default encoding in os-x for Japanese is utf-8. So i have to change encoding after pbpaste.
nkf --ic=Shift_JIS --oc=UTF-8

but utf-8 charset has more characters than shift-jis.
Is it possible to change btt default encoding setting from shift-jis to utf-8?

OSX 10.14.1 BTTT 2.660