.NET core strip and replace part of URL

I have localized website in English and German and I need to display alternate language in html head section for SEO. For example if user is browsing English version I need to add alternate link to German version in view.

string currentCulture = Thread.CurrentThread.CurrentCulture.TwoLetterISOLanguageName;

    @if (currentCulture == "en")
    {
        <link rel="alternate" href="https://example.com/de/" hreflang="de" />
    }
    else if (currentCulture == "de")
    {
        <link rel="alternate" href="https://example.com/en/" hreflang="en" />
    }

The problem is that I can get currentUrl but don’t know how to replace language part of URL to be set to opposite language.

When browsing english version currentUrl = https://example.com/en/contact/ so I need to replace /en/ part with /de/

Looking for nicest way to do this.

>Solution :

Ok since you cannot change URL as this is part of the request, what you can do is redirect to URL with correct language. Example by doing something like this:

public class LanguageRedirectMiddleware
{
    private readonly RequestDelegate _next;

    public LanguageRedirectMiddleware(RequestDelegate next)
    {
      _next = next;
    }

    public async Task Invoke(HttpContext context)
    {
        string lang = Thread.CurrentThread.CurrentCulture.TwoLetterISOLanguageName;

        // Check if the language is supported
        if (lang == "en" || lang == "de")
        {
            // Construct the language-specific URL based on the user's  language preference
            string url = $"/{lang}/{context.Request.Path}{context.Request.QueryString}";

            // Redirect to the language-specific URL
            context.Response.Redirect(url);
            return;
        }

        // Language is not supported, continue processing the request
        await _next(context);
    }
}

and in your startup.cs :

app.UseMiddleware<LanguageRedirectMiddleware>();