Add FallbackTable for localized strings table to redirect missing texts into other language

Source/Editor/Windows/Assets/LocalizedStringTableWindow.cs

@@ -113,6 +113,10 @@ namespace FlaxEditor.Windows.Assets
             [CustomEditor(typeof(FlaxEditor.CustomEditors.Editors.CultureInfoEditor))]
             public string Locale;
 
+            [EditorOrder(5), EditorDisplay("General"), Tooltip("The fallback language table to use for missing keys. Eg. table for 'en-GB' can point to 'en' as a fallback to prevent problem of missing localized strings.")]
+            [AssetReference(true)]
+            public LocalizedStringTable FallbackTable;
+
             [EditorOrder(10), EditorDisplay("Entries", EditorDisplayAttribute.InlineStyle), Tooltip("The string table. Maps the message id into the localized text. For plural messages the list contains separate items for value numbers.")]
             [Collection(Spacing = 10, OverrideEditorTypeName = "FlaxEditor.Windows.Assets.LocalizedStringTableWindow+EntryEditor")]
             public Dictionary<string, string[]> Entries;
@@ -174,6 +178,7 @@ namespace FlaxEditor.Windows.Assets
                 return;
 
             _asset.Locale = _proxy.Locale;
+            _asset.FallbackTable = _proxy.FallbackTable;
             _asset.Entries = _proxy.Entries;
             if (_asset.Save(_item.Path))
             {
@@ -200,6 +205,7 @@ namespace FlaxEditor.Windows.Assets
             _proxy = new Proxy
             {
                 Locale = _asset.Locale,
+                FallbackTable = _asset.FallbackTable,
                 Entries = _asset.Entries,
             };
             _presenter.Select(_proxy);

Source/Engine/Localization/Localization.cpp

@@ -258,20 +258,35 @@ void Localization::SetCurrentLanguageCulture(const CultureInfo& value)
 
 String Localization::GetString(const String& id, const String& fallback)
 {
-    String result;
+    const String* result = nullptr;
     for (auto& e : Instance.LocalizedStringTables)
     {
         const auto table = e.Get();
         const auto messages = table ? table->Entries.TryGet(id) : nullptr;
         if (messages && messages->Count() != 0)
         {
-            result = messages->At(0);
+            result = &messages->At(0);
             break;
         }
     }
-    if (result.IsEmpty())
-        result = fallback;
-    return result;
+    if (!result)
+    {
+        // Try using fallback tables
+        for (auto& e : Instance.LocalizedStringTables)
+        {
+            const auto table = e.Get();
+            const auto fallbackTable = table ? table->FallbackTable.Get() : nullptr;
+            const auto messages = fallbackTable ? fallbackTable->Entries.TryGet(id) : nullptr;
+            if (messages && messages->Count() != 0)
+            {
+                result = &messages->At(0);
+                break;
+            }
+        }
+    }
+    if (!result)
+        result = &fallback;
+    return *result;
 }
 
 String Localization::GetPluralString(const String& id, int32 n, const String& fallback)
@@ -289,6 +304,21 @@ String Localization::GetPluralString(const String& id, int32 n, const String& fa
             break;
         }
     }
+    if (!result)
+    {
+        // Try using fallback tables
+        for (auto& e : Instance.LocalizedStringTables)
+        {
+            const auto table = e.Get();
+            const auto fallbackTable = table ? table->FallbackTable.Get() : nullptr;
+            const auto messages = fallbackTable ? fallbackTable->Entries.TryGet(id) : nullptr;
+            if (messages && messages->Count() > n)
+            {
+                result = &messages->At(n);
+                break;
+            }
+        }
+    }
     if (!result)
         result = &fallback;
     return String::Format(result->GetText(), n);

Source/Engine/Localization/LocalizedStringTable.cpp

@@ -60,6 +60,12 @@ bool LocalizedStringTable::Save(const StringView& path)
         writer.JKEY("Locale");
         writer.String(Locale);
 
+        if (FallbackTable.GetID().IsValid())
+        {
+            writer.JKEY("FallbackTable");
+            writer.Guid(FallbackTable.GetID());
+        }
+
         writer.JKEY("Entries");
         writer.StartObject();
         for (auto& e : Entries)
@@ -102,6 +108,9 @@ Asset::LoadResult LocalizedStringTable::loadAsset()
         return result;
 
     JsonTools::GetString(Locale, *Data, "Locale");
+    Guid fallbackTable = Guid::Empty;
+    JsonTools::GetGuid(fallbackTable, *Data, "FallbackTable");
+    FallbackTable = fallbackTable;
     const auto entriesMember = SERIALIZE_FIND_MEMBER((*Data), "Entries");
     if (entriesMember != Data->MemberEnd() && entriesMember->value.IsObject())
     {
@@ -134,5 +143,6 @@ void LocalizedStringTable::unload(bool isReloading)
     JsonAssetBase::unload(isReloading);
 
     Locale.Clear();
+    FallbackTable = nullptr;
     Entries.Clear();
 }

Source/Engine/Localization/LocalizedStringTable.h

@@ -5,6 +5,7 @@
 #include "Engine/Content/JsonAsset.h"
 #include "Engine/Core/Collections/Array.h"
 #include "Engine/Core/Collections/Dictionary.h"
+#include "Engine/Scripting/SoftObjectReference.h"
 
 /// <summary>
 /// Contains localized strings table for a given culture.
@@ -14,17 +15,24 @@ API_CLASS(NoSpawn) class FLAXENGINE_API LocalizedStringTable : public JsonAssetB
 {
 DECLARE_ASSET_HEADER(LocalizedStringTable);
 public:
+
     /// <summary>
     /// The locale of the localized string table (eg. pl-PL).
     /// </summary>
     API_FIELD() String Locale;
 
+    /// <summary>
+    /// The fallback language table to use for missing keys. Eg. table for 'en-GB' can point to 'en' as a fallback to prevent problem of missing localized strings.
+    /// </summary>
+    API_FIELD() SoftObjectReference<LocalizedStringTable> FallbackTable;
+
     /// <summary>
     /// The string table. Maps the message id into the localized text. For plural messages the list contains separate items for value numbers.
     /// </summary>
     API_FIELD() Dictionary<String, Array<String>> Entries;
 
 public:
+
     /// <summary>
     /// Adds the localized string to the table.
     /// </summary>