This has come up before; I think https://lists.w3.org/Archives/Public/public-whatwg-archive/2014Feb/0075.html is the most recent thread on the subject. In general, the spec does not mandate such UI features of browsers, but the input types are somewhat of a gray area in that regard, since part of their purpose is specifically to give better UI presentation.
My suggestion during that thread was to delegate to ES's i18n API: https://lists.w3.org/Archives/Public/public-whatwg-archive/2014Feb/0094.html In general, this type of thing is hard to get support for these days. Implementers are more interested in getting stuff like web components in place so that authors can produce better controls, without waiting for them to be debated, standardized, and implemented everywhere. I think it'd be a worthwhile improvement, especially since custom elements are unable to participate in the form control ecosystem (constraint validation, form submission, etc.). But we're going to need implementer interest before anything gets done here. Soooo ... any implementers interested in solving this problem?
