In most cases, you'd want this to be handled at the OS-level by setting your locale preferences to match your region. However, this would require the app to be properly internationalized (using number formatters, etc.) to work correctly.

So you bring up a neat idea. I'm not sure which OSs support it, but OpenType does have a `locale` feature, primarily for glyph variants (ex: same codepoint, but different glyph for Chinese vs. Japanese). I'm guessing it could be abused to accomplish what you want and not require an app to adopt i18n APIs.