When using "createElementSelectorModal()" how do you respect selected locale?
The BaseElementSelectorModal class takes a second parameter settings, which can include a criteria object. This criteria object is used to create an ElementCriteriaModel on the server, which means it can have any property an ElementCriteriaModel can have – including locale:

var currentLocale = Craft.getLocalStorage('BaseElementIndex.locale') || Craft.locale;

var modal = Craft.createElementSelectorModal('Entry', {
    criteria : {
        locale : currentLocale
    }
});