Field's TitleResource.SetValueForUICulture() does not work for the web's default language

Question

I have a site column in my site collection whose title I change / translate with following PowerShell statement:

$w = Get-SPWeb "URL to the site collection"
$f = $w.Fields.GetFieldByInternalName("InternalFieldName")
foreach ($c in $w.SupportedUICultures)
{
  $f.TitleResource.SetValueForUICulture($c, "Title for $($c.Name)")
}

$f.Update() /* or */ $f.TitleResource.Update()

That works pretty fine for all alternate languages but the default language.

Suppose there is a root web with a default language en-US and two alternate languages de-DE and tr-TR. Further suppose the field fhas a title of "Default Title" in all three languages. After running the script the field f has the title "Title for de-DE" when German is selected as the language in the UI. In analogy fhas the title "Title for tr-TR" when the user selects Turkish as the language. If the default language is selcted the title is shown as "Default Title".

Suppose that de-DE is the default language then the title of f is "Default Title", "Title for en-US", and "Title for tr-TR".

So the resource for the default language was not changed. Why?

Answer 1

As per this article and that one, it seems you cannot set the resource for the default language of the Web with SetValueForUICulture. So, now, my own code looks like:

    private void LocalizeDisplayName(SPField field, Dictionary<int, string> localizedDisplayNames)
    {
        if ((field == null) || (localizedDisplayNames == null) || (localizedDisplayNames.Count == 0))
            return;

        foreach (KeyValuePair<int, string> kvp in localizedDisplayNames)
        {
            field.TitleResource.SetValueForUICulture(new CultureInfo(kvp.Key), kvp.Value);
            if (field.ParentList.ParentWeb.Language == kvp.Key) // Default language cannot be set with SetValueForUICulture, see https://social.msdn.microsoft.com/Forums/sharepoint/en-US/6abbe88b-1111-4406-8716-d57b1600a687/titleresources-setvalueforuiculture-for-default-language?forum=sharepointdevelopmentlegacy
            {
                field.Title = kvp.Value;
                field.Update();
            }
        }

        field.TitleResource.Update();
    }