Translate the ISO-639-2/B codes to ISO-639-2/T. (#13068)

* Translate the ISO-639-2/B codes to ISO-639-2/T.

This enables 19 additional languages to be displayed correctly.

* Convert the 2-dimensional array to a dictionary

* Added the French language to the list of ISO-639-2/B codes

* Don't change the property, use a local variable instead.

* When creating the MediaStream in the MediaStreamRepository ensure that the ISO 639-2/T (f.e. deu) code is used for the language as that is the one the .NET culture info knows.
The other code is most likely the ISO 639-2/B code (f.e. ger) which is unknown to the .NET culture info and will result in just displaying the code instead of the display name.

* Move the substitution of ISO 639-2/B to /T to the localization manager.
Some language (like Chinese) have multiple entries in the iso6392.txt file (f.e. zho|chi|zh|..., zho|chi|zh-tw|...) but the conversation between /T and /B is the same so use .TryAdd.

* Change the method definition from GetISO6392TFromB to TryGetISO6392TFromB and return true if a case was found.

* Add unit tests for TryGetISO6392TFromB.

tests/Jellyfin.Server.Implementations.Tests/Localization/LocalizationManagerTests.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Linq;
 using System.Threading.Tasks;
+using BitFaster.Caching;
 using Emby.Server.Implementations.Localization;
 using MediaBrowser.Controller.Configuration;
 using MediaBrowser.Model.Configuration;
@@ -51,6 +52,30 @@ namespace Jellyfin.Server.Implementations.Tests.Localization
             Assert.Contains("ger", germany.ThreeLetterISOLanguageNames);
         }
 
+        [Fact]
+        public async Task TryGetISO6392TFromB_Success()
+        {
+            var localizationManager = Setup(new ServerConfiguration
+            {
+                UICulture = "de-DE"
+            });
+            await localizationManager.LoadAll();
+
+            string? isoT;
+
+            // Translation ger -> deu
+            Assert.True(localizationManager.TryGetISO6392TFromB("ger", out isoT));
+            Assert.Equal("deu", isoT);
+
+            // chi -> zho
+            Assert.True(localizationManager.TryGetISO6392TFromB("chi", out isoT));
+            Assert.Equal("zho", isoT);
+
+            // eng is already ISO 639-2/T
+            Assert.False(localizationManager.TryGetISO6392TFromB("eng", out isoT));
+            Assert.Null(isoT);
+        }
+
         [Theory]
         [InlineData("de")]
         [InlineData("deu")]