Using RouteDataRequestCultureProvider in asp net core 3.1

So I ended up fixing this problem by overriding how the anchor tag helper works and making sure it always passes in the culture from the route.

This is the custom tag helper:

[HtmlTargetElement("a", Attributes = ActionAttributeName)]
[HtmlTargetElement("a", Attributes = ControllerAttributeName)]
[HtmlTargetElement("a", Attributes = AreaAttributeName)]
[HtmlTargetElement("a", Attributes = PageAttributeName)]
[HtmlTargetElement("a", Attributes = PageHandlerAttributeName)]
[HtmlTargetElement("a", Attributes = FragmentAttributeName)]
[HtmlTargetElement("a", Attributes = HostAttributeName)]
[HtmlTargetElement("a", Attributes = ProtocolAttributeName)]
[HtmlTargetElement("a", Attributes = RouteAttributeName)]
[HtmlTargetElement("a", Attributes = RouteValuesDictionaryName)]
[HtmlTargetElement("a", Attributes = RouteValuesPrefix + "*")]
public class CultureAnchorTagHelper : AnchorTagHelper
{
    private const string ActionAttributeName = "asp-action";
    private const string ControllerAttributeName = "asp-controller";
    private const string AreaAttributeName = "asp-area";
    private const string PageAttributeName = "asp-page";
    private const string PageHandlerAttributeName = "asp-page-handler";
    private const string FragmentAttributeName = "asp-fragment";
    private const string HostAttributeName = "asp-host";
    private const string ProtocolAttributeName = "asp-protocol";
    private const string RouteAttributeName = "asp-route";
    private const string RouteValuesDictionaryName = "asp-all-route-data";
    private const string RouteValuesPrefix = "asp-route-";


    public CultureAnchorTagHelper(IHtmlGenerator generator, IHttpContextAccessor contextAccessor) : base(generator)
    {
        var culture = contextAccessor.HttpContext.Request.RouteValues["culture"]?.ToString() ?? "en";
        RouteValues["culture"] = culture;
    }
}

To use it you need to remove the default anchor tag helper and add your own in _ViewImports.cshtml:

@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
@removeTagHelper Microsoft.AspNetCore.Mvc.TagHelpers.AnchorTagHelper, Microsoft.AspNetCore.Mvc.TagHelpers
@addTagHelper *, Your.Assembly.Namespace //assembly name containing class above

Some useful links:

• anchor tag source code
• tag helpers
• extending tag helpers