I'm using ZP 1.4.12 with "Multi-lingual" enabled. To switch between languages I've enabled the "dynamic-locale" plugin as well as "seo_locale" (i.e. I don't use subdomains).
Switching between languages by clicking on the flags works fine in Firefox 46, but fails in Internet Explorer 11. When changing the preferred language in IE's Internet Options the selected language is used by ZP, i.e. localization generally works. But for some reason clicks on the flags are ignored.