redmine/public/stylesheets/context_menu_rtl.css

#context-menu li.folder ul { left:auto; right:168px; }
#context-menu li.folder>ul { left:auto; right:148px; }
#context-menu li a.submenu { background:url("../images/arrow_left.png") left no-repeat; }

#context-menu a {
   background-position: 100% 40%;
   padding-right: 20px;
   padding-left: 0px;
}