Umbraco.AssignedContentItem.GetCultureFromDomains() no longer returns the correct culture in V15.0.0

Which Umbraco version are you using? (Please write the exact version, example: 10.1.0)

15.0.0

Bug summary

I upgraded a simple project from v14 to v15 and now the language switch functionality no longer works correctly. Umbraco.AssignedContentItem.GetCultureFromDomains() seems to always returns 'en-US' even when I'm on a page in another language (zh-Hans).

Specifics

No response

Steps to reproduce

Set-up a multilingual site with two languages.

Configure 'culture and host names' on the root node.

Add code for the language switch to the page similar to the docs.

@using Umbraco.Cms.Web.Common
@inherits Umbraco.Cms.Web.Common.Views.UmbracoViewPage<IBasePage>

@{
    var homePage = Umbraco.ContentAtRoot()
        .FirstOrDefault(c => c.ContentType.Alias == WebsiteFolder.ModelTypeAlias)
        ?.FirstChild(c => c.ContentType.Alias == HomePage.ModelTypeAlias);

    if (homePage is null)
    {
        return;
    }

    var cultures = homePage.Cultures;

    if (cultures.Count > 1)
    {
        <ul aria-label="Language switcher">
            @foreach (var cult in cultures)
            {
                //get the settings for this culture
                var culture = new System.Globalization.CultureInfo(cult.Key);

                //if the current page has a language variant, otherwise link to the homepage language variant
                string langUrl = Umbraco.AssignedContentItem.Url(cult.Key, UrlMode.Relative);
                if (string.IsNullOrWhiteSpace(langUrl) || langUrl == "#")
                {
                    langUrl = homePage.Url(cult.Key, UrlMode.Relative);
                }

                <li>
                    @if (cult.Key.ToLower() == Umbraco.AssignedContentItem.GetCultureFromDomains()?.ToLower())
                    {
                        <span aria-current="true">@culture.TwoLetterISOLanguageName</span>
                    }
                    else
                    {
                        <a href="@langUrl" hreflang="@cult.Key" lang="@cult.Key">@culture.TwoLetterISOLanguageName</a>
                    }
                </li>
            }
        </ul>
    }
}

Expected result / actual result

The language switch should allow you to switch back and forth between the two language versions of the home page. You can switch successfully from English to Chinese. But when you are on the Chinese version of the page the language switch does not allow you to switch back to English because GetCultureFromDomains() always returns 'en-US' and it should be 'zh-Hans'.

Correct language switch on the English version.

Incorrect language switch on the Chinese version.

Hi there @Manny-GitHub!

Firstly, a big thank you for raising this issue. Every piece of feedback we receive helps us to make Umbraco better.

We really appreciate your patience while we wait for our team to have a look at this but we wanted to let you know that we see this and share with you the plan for what comes next.

We'll assess whether this issue relates to something that has already been fixed in a later version of the release that it has been raised for.
If it's a bug, is it related to a release that we are actively supporting or is it related to a release that's in the end-of-life or security-only phase?
We'll replicate the issue to ensure that the problem is as described.
We'll decide whether the behavior is an issue or if the behavior is intended.

We wish we could work with everyone directly and assess your issue immediately but we're in the fortunate position of having lots of contributions to work with and only a few humans who are able to do it. We are making progress though and in the meantime, we will keep you in the loop and let you know when we have any questions.

Thanks, from your friendly Umbraco GitHub bot :robot: :slightly_smiling_face:

umbraco / Umbraco-CMS