Include Custom Taxon Properties in Sitefinity's Index

CustomConcatenationTranslator.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web;
using Telerik.OpenAccess;
using Telerik.Sitefinity.Publishing.Translators;
using Telerik.Sitefinity.Taxonomies;
using Telerik.Sitefinity.Taxonomies.Model;

namespace SitefinityWebApp.Search
{
    public class CustomConcatenationTranslator : ConcatenationTranslator
    {
        internal static void Register()
        {
            PipeTranslatorFactory.RegisterTranslator(new CustomConcatenationTranslator());
        }

        public override object Translate(object[] data, IDictionary<string, string> translationSettings)
        {
            if (data != null && data.Length > 0)
            {
                List<object> translated = new List<object>();
                for (int i = 0; i < data.Length; i++)
                {
                    if (data[i] is TrackedList<Guid>)
                    {
                        data[i] = CustomTransparentTranslator.TranslateTrackedList(data[i] as TrackedList<Guid>);
                    }
                }
            }
            return base.Translate(data, translationSettings);
        }
    }
}

CustomHtmlStripperTranslator.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using Telerik.OpenAccess;
using Telerik.Sitefinity.Publishing.Translators;

namespace SitefinityWebApp.Search
{
    public class CustomHtmlStripperTranslator : HtmlStripperTranslator
    {
        internal static void Register()
        {
            PipeTranslatorFactory.RegisterTranslator(new CustomHtmlStripperTranslator());
        }

        public override object Translate(object[] data, IDictionary<string, string> translationSettings)
        {
            if (data != null && data.Length > 0)
            {
                for (int i = 0; i < data.Length; i++)
                {
                    if (data[i] is TrackedList<Guid>)
                    {
                        data[i] = CustomTransparentTranslator.TranslateTrackedList(data[i] as TrackedList<Guid>);
                    }
                }
            }
            return base.Translate(data, translationSettings);
        }
    }
}

CustomTransparentTranslator.cs

using System;
using System.Collections.Generic;
using System.Text;
using Telerik.OpenAccess;
using Telerik.Sitefinity.Model;
using Telerik.Sitefinity.Publishing;
using Telerik.Sitefinity.Publishing.Translators;
using Telerik.Sitefinity.Taxonomies;
using Telerik.Sitefinity.Taxonomies.Model;

namespace SitefinityWebApp.Search
{
    public class CustomTransparentTranslator : TransparentTranslator
    {
        internal static void Register()
        {
            PipeTranslatorFactory.RegisterTranslator(new CustomTransparentTranslator());
        }

        public override object Translate(object[] data, IDictionary<string, string> translationSettings)
        {
            if (data != null && data.Length > 0)
            {
                List<object> translated = new List<object>();
                for (int i = 0; i < data.Length; i++)
                {
                    if (data[i] is TrackedList<Guid>)
                    {
                        data[i] = CustomTransparentTranslator.TranslateTrackedList(data[i] as TrackedList<Guid>);
                    }
                }
            }
            return base.Translate(data, translationSettings);
        }

        internal static void AddTagIds(WrapperObject item, IDataItem data)
        {
            var props = item.AdditionalProperties;
            var tags = data.GetPropertyValue<TrackedList<Guid>>(PublishingConstants.FieldTags);

            if (tags != null)
            {
                props[PublishingConstants.FieldTags] = TranslateTrackedList(tags);
            }
        }

        internal static object TranslateTrackedList(TrackedList<Guid> list)
        {
            if (list == null || list.Count == 0)
            {
                return null;
            }
            string title;
            StringBuilder sb = new StringBuilder();
            TaxonomyManager mgr = TaxonomyManager.GetManager();
            foreach (var id in list)
            {
                ITaxon t = mgr.GetTaxon(id);
                if (t != null)
                {
                    title = t.Title;
                    if (!string.IsNullOrWhiteSpace(title))
                    {
                        if (sb.Length > 0)
                        {
                            sb.Append(" ").Append(title);
                        }
                        else
                        {
                            sb.Append(title);
                        }
                    }
                    if (sb.Length > 0)
                    {
                        sb.Append(" ").Append(id);
                    }
                    else
                    {
                        sb.Append(id);
                    }
                }
            }
            return sb.Length > 0 ? (object)sb.ToString() : list;
        }
    }
}

NOTE: I had to add the CustomHtmlStripperTranslator due to a bug in Sitefinity v7.3.5619.0 where hierarchical taxonomies are now being handled by the HtmlStripperTranslator. So now you need to register both (Transparent & HtmlStripper).