CultureNotFound when formatting with CultureInfo at Azure

Question

This method is used to auto-generate some Html fields to reduce code duplication. It works perfectly fine when I host it locally:

static string GenerateTextField<DBType, FieldType>(this HtmlHelper<DBType> 
page, Expression<Func<DBType, FieldType>> fieldExp, string formControlData)
{
        var model = page.ViewData.Model;

        var fieldName = 
            ExpressionHelper.GetExpressionText(fieldExp).Split('.').Last();
        var formatRules = new CultureInfo("en-EN");
        string valueText = "";

        var value = model != null?
            fieldExp.Compile()(model): 
            default(FieldType);
        if (typeof(FieldType).IsAssignableFrom(typeof(float))) valueText = 
            ((float)(object)value).ToString(formatRules);
        else valueText = value?.ToString();

        System.Diagnostics.Debug.WriteLine("valueText =" + valueText);

        return [html text, converted to MvcHtmlString elsewhere];
}

However, when I export it to be hosted by Azure web app and run it there, it announces: Culture is not supported. Parameter name: name en-EN is an invalid culture identifier.

I am aware of the topic Culture is suddenly not supported anymore on Azure web app. The problem is that the remedy suggested there concetrates on how to build a RegionInfo, which I'm not even using.

I need that formatting with english culture because the html field uses a custom numeric spinner which tructates the database value if it is entered with a decimal comma instead of a decimal point.

I can of course format the string by hand, but is there a better solution?