5 files changed, 78 insertions, 12 deletions
diff --git a/src/api/wix/WixToolset.Data/Localization.cs b/src/api/wix/WixToolset.Data/Localization.cs
index 70c096de..d7727f17 100644
--- a/src/api/wix/WixToolset.Data/Localization.cs
+++ b/src/api/wix/WixToolset.Data/Localization.cs
@@ -16,10 +16,19 @@ namespace WixToolset.Data
        private readonly Dictionary<string, LocalizedControl> localizedControls = new Dictionary<string, LocalizedControl>();
        /// <summary>
+        /// Instantiates a new localization object with default location.
+        /// </summary>
+        public Localization(int? codepage, int? summaryInformationCodepage, string culture, IDictionary<string, BindVariable> variables, IDictionary<string, LocalizedControl> localizedControls) : 
+            this(LocalizationLocation.Source, codepage, summaryInformationCodepage, culture, variables, localizedControls)
+        {
+        }
+        /// <summary>
        /// Instantiates a new localization object.
        /// </summary>
-        public Localization(int? codepage, int? summaryInformationCodepage, string culture, IDictionary<string, BindVariable> variables, IDictionary<string, LocalizedControl> localizedControls)
+        public Localization(LocalizationLocation location, int? codepage, int? summaryInformationCodepage, string culture, IDictionary<string, BindVariable> variables, IDictionary<string, LocalizedControl> localizedControls)
        {
+            this.Location = location;
            this.Codepage = codepage;
            this.SummaryInformationCodepage = summaryInformationCodepage;
            this.Culture = culture?.ToLowerInvariant() ?? String.Empty;
@@ -28,6 +37,11 @@ namespace WixToolset.Data
        }
        /// <summary>
+        /// Gets the location the localization came from.
+        /// </summary>
+        public LocalizationLocation Location { get; private set; }
+        /// <summary>
        /// Gets the codepage.
        /// </summary>
        /// <value>The codepage.</value>
@@ -57,9 +71,27 @@ namespace WixToolset.Data
        /// <value>The localized controls.</value>
        public ICollection<KeyValuePair<string, LocalizedControl>> LocalizedControls => this.localizedControls;
+        /// <summary>
+        /// Updates the location, if the location is a higher state than the current state.
+        /// </summary>
+        /// <param name="location">Location to update to.</param>
+        /// <returns>This localization object.</returns>
+        public Localization UpdateLocation(LocalizationLocation location)
+        {
+            if (this.Location < location)
+            {
+                this.Location = location;
+            }
+            return this;
+        }
        internal JsonObject Serialize()
        {
-            var jsonObject = new JsonObject();
+            var jsonObject = new JsonObject()
+            {
+                { "location", this.Location.ToString().ToLowerInvariant() }
+            };
            if (this.Codepage.HasValue)
            {
@@ -108,6 +140,7 @@ namespace WixToolset.Data
        internal static Localization Deserialize(JsonObject jsonObject)
        {
+            var location = jsonObject.GetEnumOrDefault("location", LocalizationLocation.Source);
            var codepage = jsonObject.GetValueOrDefault("codepage", null);
            var summaryCodepage = jsonObject.GetValueOrDefault("summaryCodepage", null);
            var culture = jsonObject.GetValueOrDefault<string>("culture");
@@ -131,7 +164,7 @@ namespace WixToolset.Data
                }
            }
-            return new Localization(codepage, summaryCodepage, culture, variables, controls);
+            return new Localization(location, codepage, summaryCodepage, culture, variables, controls);
        }
    }
 }
diff --git a/src/api/wix/WixToolset.Data/LocalizationLocation.cs b/src/api/wix/WixToolset.Data/LocalizationLocation.cs
new file mode 100644
index 00000000..773c4d9f
--- /dev/null
+++ b/src/api/wix/WixToolset.Data/LocalizationLocation.cs
@@ -0,0 +1,31 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the Microsoft Reciprocal License. See LICENSE.TXT file in the project root for full license information.
+namespace WixToolset.Data
+{
+    /// <summary>
+    /// Location where the localization was loaded.
+    /// </summary>
+    public enum LocalizationLocation
+    {
+        /// <summary>
+        /// Localization loaded from .wxl source file.
+        /// </summary>
+        Source,
+        /// <summary>
+        /// Localization loaded from .wixlib library.
+        /// </summary>
+        Library,
+        /// <summary>
+        /// Localization loaded from .wixlib library within .wixext WixExtension.
+        /// </summary>
+        Extension,
+        /// <summary>
+        /// Localization placed in .wixext WixExtension as the default culture localization for the
+        /// WixExtension.
+        /// </summary>
+        ExtensionDefaultCulture
+    }
+}
diff --git a/src/api/wix/WixToolset.Data/LocalizedControl.cs b/src/api/wix/WixToolset.Data/LocalizedControl.cs
index 1252842b..9f59ce46 100644
--- a/src/api/wix/WixToolset.Data/LocalizedControl.cs
+++ b/src/api/wix/WixToolset.Data/LocalizedControl.cs
@@ -45,7 +45,10 @@ namespace WixToolset.Data
        /// Get key for a localized control.
        /// </summary>
        /// <returns>The localized control id.</returns>
-        public string GetKey() => LocalizedControl.GetKey(this.Dialog, this.Control);
+        public string GetKey()
+        {
+            return LocalizedControl.GetKey(this.Dialog, this.Control);
+        }
        /// <summary>
        /// Get key for a localized control.
@@ -53,7 +56,10 @@ namespace WixToolset.Data
        /// <param name="dialog">The optional id of the control's dialog.</param>
        /// <param name="control">The id of the control.</param>
        /// <returns>The localized control id.</returns>
-        public static string GetKey(string dialog, string control) => String.Concat(dialog, "/", control);
+        public static string GetKey(string dialog, string control)
+        {
+            return String.Concat(dialog, "/", control);
+        }
        internal JsonObject Serialize()
        {
diff --git a/src/api/wix/WixToolset.Extensibility/BaseExtensionData.cs b/src/api/wix/WixToolset.Extensibility/BaseExtensionData.cs
index e4a10fd9..291b1014 100644
--- a/src/api/wix/WixToolset.Extensibility/BaseExtensionData.cs
+++ b/src/api/wix/WixToolset.Extensibility/BaseExtensionData.cs
@@ -2,6 +2,7 @@
 namespace WixToolset.Extensibility
 {
+    using System;
    using WixToolset.Data;
    /// <summary>
@@ -10,8 +11,9 @@ namespace WixToolset.Extensibility
    public abstract class BaseExtensionData : IExtensionData
    {
        /// <summary>
-        /// See <see cref="IExtensionData.DefaultCulture"/>
+        /// Obsolete in WiX v5. Use the WixLocalization/@ExtensionDefaultCulture attribute in the wxl file instead.
        /// </summary>
+        [Obsolete("Set the ExtensionDefaultCulture attribute in the WixLocalization source file instead.")]
        public virtual string DefaultCulture => null;
        /// <summary>
diff --git a/src/api/wix/WixToolset.Extensibility/IExtensionData.cs b/src/api/wix/WixToolset.Extensibility/IExtensionData.cs
index 823e2beb..e6565f4a 100644
--- a/src/api/wix/WixToolset.Extensibility/IExtensionData.cs
+++ b/src/api/wix/WixToolset.Extensibility/IExtensionData.cs
@@ -10,12 +10,6 @@ namespace WixToolset.Extensibility
    public interface IExtensionData
    {
        /// <summary>
-        /// Gets the optional default culture.
-        /// </summary>
-        /// <value>The optional default culture.</value>
-        string DefaultCulture { get; }
-        /// <summary>
        ///
        /// </summary>
        /// <param name="name"></param>