Go to Keyboard Preferences, Layouts tab, Add button. Now you whould have the "Choose a Layout window" open.  If you now want to select a keyboard layout, you just go throug the list box and CLICK on the one you want. However, in nearly all other applications that use list boxes, it is possible to just click in the List box and then type the first letter of the layout you want. 

For instance, if you want to select "Bulgarian" you should be able to just click once in the list box and then press "B" on the keyboard. Or to start typing "Bul.." very fast; and then Bulgarian should get selected. 


I hope this explanation makes sense. If not, it is just like forms where you have to select your state or country from a list. Usually you (or I) do not go through the whole list to look for my state. I just type click in the list box and press "P" on the keyboard for Pennsylvania (the only US state starting with P) and it gets selected right away.