How do I change my navbar from "left to right" to "right to left"?
Note: Following answer is for D7, but the concept is same for D8 also I think, if you want to do using CSS, Just you need to apply the same logic where to apply CSS float: left; and float: right;.   

This you can do with CSS. 

If there is just a menu with list of items, you can do easily with float: right at appropriate place.

But, bootstrap's default nav-bar contains Logo Site name primary-menu and Secondary-menu, Hence css will be some complicated.

Now, I have used the following set (LTR Default), 


  


And after looking their HTML I have applied following CSS,

.navbar {
    .navbar-header {float: right;
        a.logo { float: right !important;}
    }
    .navbar-collapse{
        nav {

            ul.menu.navbar-nav {float: right;
                li {
                    float: right;
                }
            }
            ul.menu.navbar-nav.secondary {float: left !important;
                li {
                    float: right;
                }
            }

        }
    }
}


After applying the CSS, It has arranged in such a way.


  


If you slightly practice, you can by yourself come to know how it works, it is easy.