ASP.NET Core Request Localization Options

Here is my custom request culture provider which returns “en” as a default culture if no culture specified in url (for example http://sypalo.com/ru or http://sypalo.com/en).
My idea to show website on that language which is default in user’s browser, so I’m looking a way how to determine it and return it instead of: return Task.FromResult(new ProviderCultureResult(“en”, “en”));