selectAll.click(function(){
     langs.prop('checked',this.checked);
     selectAllLabel.toggle(!this.checked);
     deselectAllLabel.toggle(this.checked);
});
invertSelect.click(()=>langs.click());
langs.click(function(){
     var isAllChecked=langs.map(function(){return this.checked;}).get().reduce((x,y)=>x&&y);
     if(isAllChecked||selectAll.is(":checked")){
         selectAll.prop('checked',isAllChecked);
         selectAllLabel.toggle(!isAllChecked);
         deselectAllLabel.toggle(isAllChecked);
     }
});