With GT4T version 4.22, you can select some source text and press CTRL twice quickly as the hot key! I find it much more convenient than the usual CTRL+J. Do try it!
It’s quicker because after your left hand are pressing the CTRL and SHIFT key while your right hand are pressing the LEFT or RIGHT arrow to make a selection, you can immediately hit CTRL button twice again to get the translation and you don’t need to use your right hand to get the J button.
Yes, always use keyboards to make a selection (CTRL+SHIFT+LEFT or RIGHT arrow), not the mouse!
To use the new hot keys, go to Hot Keys -> Redefine and then check the boxes before “Press CTRL twice” and “Press SHIFT twice”