Fix language display for ISO 639-2-only codes (e.g. mul, und)

LoadCultures() in LocalizationManager skipped all iso6392.txt entries
without a two-letter ISO 639-1 code, dropping 302 of 496 languages
including mul (Multiple languages), und (Undetermined), mis (Uncoded
languages), zxx, and many real languages like Achinese, Akkadian, etc.
This caused FindLanguageInfo() to return null for these codes, which
meant:
- ExternalPathParser could not recognize them as valid language codes
  in subtitle filenames, so the Language field was never set
- DisplayTitle fell back to the raw code string (e.g. "Mul")

Fix by allowing entries without two-letter codes to be loaded with an
empty TwoLetterISOLanguageName. Also set LocalizedLanguage in
ProbeResultNormalizer for ffprobe-detected streams (the DB repository
path was already handled on master).

4 files changed, 27 insertions, 3 deletions

diff --git a/Emby.Server.Implementations/Localization/LocalizationManager.cs b/Emby.Server.Implementations/Localization/LocalizationManager.cs
index bc80c2b405..6fca5bc1ba 100644
--- a/Emby.Server.Implementations/Localization/LocalizationManager.cs
+++ b/Emby.Server.Implementations/Localization/LocalizationManager.cs
@@ -138,7 +138,7 @@ namespace Emby.Server.Implementations.Localization
                     string twoCharName = parts[2];
                     if (string.IsNullOrWhiteSpace(twoCharName))
                     {
-                        continue;
+                        twoCharName = string.Empty;
                     }
                     else if (twoCharName.Contains('-', StringComparison.OrdinalIgnoreCase))
                     {
diff --git a/MediaBrowser.MediaEncoding/Probing/ProbeResultNormalizer.cs b/MediaBrowser.MediaEncoding/Probing/ProbeResultNormalizer.cs
index d3e7b52315..203e72de36 100644
--- a/MediaBrowser.MediaEncoding/Probing/ProbeResultNormalizer.cs
+++ b/MediaBrowser.MediaEncoding/Probing/ProbeResultNormalizer.cs
@@ -729,6 +729,9 @@ namespace MediaBrowser.MediaEncoding.Probing
                 stream.Type = MediaStreamType.Audio;
                 stream.LocalizedDefault = _localization.GetLocalizedString("Default");
                 stream.LocalizedExternal = _localization.GetLocalizedString("External");
+                stream.LocalizedLanguage = !string.IsNullOrEmpty(stream.Language)
+                    ? _localization.FindLanguageInfo(stream.Language)?.DisplayName
+                    : null;
 
                 stream.Channels = streamInfo.Channels;
 
@@ -767,6 +770,9 @@ namespace MediaBrowser.MediaEncoding.Probing
                 stream.LocalizedForced = _localization.GetLocalizedString("Forced");
                 stream.LocalizedExternal = _localization.GetLocalizedString("External");
                 stream.LocalizedHearingImpaired = _localization.GetLocalizedString("HearingImpaired");
+                stream.LocalizedLanguage = !string.IsNullOrEmpty(stream.Language)
+                    ? _localization.FindLanguageInfo(stream.Language)?.DisplayName
+                    : null;
 
                 if (string.IsNullOrEmpty(stream.Title))
                 {
diff --git a/MediaBrowser.Model/Entities/MediaStream.cs b/MediaBrowser.Model/Entities/MediaStream.cs
index 11f81ff7d8..4491fb5ace 100644
--- a/MediaBrowser.Model/Entities/MediaStream.cs
+++ b/MediaBrowser.Model/Entities/MediaStream.cs
@@ -5,7 +5,6 @@ using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Globalization;
-using System.Linq;
 using System.Text;
 using System.Text.Json.Serialization;
 using Jellyfin.Data.Enums;
diff --git a/tests/Jellyfin.Server.Implementations.Tests/Localization/LocalizationManagerTests.cs b/tests/Jellyfin.Server.Implementations.Tests/Localization/LocalizationManagerTests.cs
index e60522bf78..700ac5dced 100644
--- a/tests/Jellyfin.Server.Implementations.Tests/Localization/LocalizationManagerTests.cs
+++ b/tests/Jellyfin.Server.Implementations.Tests/Localization/LocalizationManagerTests.cs
@@ -41,7 +41,7 @@ namespace Jellyfin.Server.Implementations.Tests.Localization
             await localizationManager.LoadAll();
             var cultures = localizationManager.GetCultures().ToList();
 
-            Assert.Equal(194, cultures.Count);
+            Assert.Equal(496, cultures.Count);
 
             var germany = cultures.FirstOrDefault(x => x.TwoLetterISOLanguageName.Equals("de", StringComparison.Ordinal));
             Assert.NotNull(germany);
@@ -99,6 +99,25 @@ namespace Jellyfin.Server.Implementations.Tests.Localization
             Assert.Contains("ger", germany.ThreeLetterISOLanguageNames);
         }
 
+        [Theory]
+        [InlineData("mul", "Multiple languages")]
+        [InlineData("und", "Undetermined")]
+        [InlineData("mis", "Uncoded languages")]
+        [InlineData("zxx", "No linguistic content; Not applicable")]
+        public async Task FindLanguageInfo_ISO6392Only_Success(string code, string expectedDisplayName)
+        {
+            var localizationManager = Setup(new ServerConfiguration
+            {
+                UICulture = "en-US"
+            });
+            await localizationManager.LoadAll();
+
+            var culture = localizationManager.FindLanguageInfo(code);
+            Assert.NotNull(culture);
+            Assert.Equal(expectedDisplayName, culture.DisplayName);
+            Assert.Equal(code, culture.ThreeLetterISOLanguageName);
+        }
+
         [Fact]
         public async Task GetParentalRatings_Default_Success()
         {