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.

Emby.Server.Implementations/Localization/LocalizationManager.cs

@@ -1,6 +1,8 @@
 using System;
 using System.Collections.Concurrent;
+using System.Collections.Frozen;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
 using System.Reflection;
@@ -38,6 +40,8 @@ namespace Emby.Server.Implementations.Localization
 
         private List<CultureDto> _cultures = [];
 
+        private FrozenDictionary<string, string> _iso6392BtoT = null!;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="LocalizationManager" /> class.
         /// </summary>
@@ -100,6 +104,7 @@ namespace Emby.Server.Implementations.Localization
         private async Task LoadCultures()
         {
             List<CultureDto> list = [];
+            Dictionary<string, string> iso6392BtoTdict = new Dictionary<string, string>();
 
             using var stream = _assembly.GetManifestResourceStream(CulturesPath);
             if (stream is null)
@@ -142,12 +147,17 @@ namespace Emby.Server.Implementations.Localization
                     else
                     {
                         threeLetterNames = [parts[0], parts[1]];
+
+                        // In cases where there are two TLN the first one is ISO 639-2/T and the second one is ISO 639-2/B
+                        // We need ISO 639-2/T for the .NET cultures so we cultivate a dictionary for the translation B->T
+                        iso6392BtoTdict.TryAdd(parts[1], parts[0]);
                     }
 
                     list.Add(new CultureDto(name, name, twoCharName, threeLetterNames));
                 }
 
                 _cultures = list;
+                _iso6392BtoT = iso6392BtoTdict.ToFrozenDictionary(StringComparer.OrdinalIgnoreCase);
             }
         }
 
@@ -505,5 +515,26 @@ namespace Emby.Server.Implementations.Localization
             yield return new LocalizationOption("漢語 (繁體字)", "zh-TW");
             yield return new LocalizationOption("廣東話 (香港)", "zh-HK");
         }
+
+        /// <inheritdoc />
+        public bool TryGetISO6392TFromB(string isoB, [NotNullWhen(true)] out string? isoT)
+        {
+            // Unlikely case the dictionary is not (yet) initialized properly
+            if (_iso6392BtoT == null)
+            {
+                isoT = null;
+                return false;
+            }
+
+            var result = _iso6392BtoT.TryGetValue(isoB, out isoT) && !string.IsNullOrEmpty(isoT);
+
+            // Ensure the ISO code being null if the result is false
+            if (!result)
+            {
+                isoT = null;
+            }
+
+            return result;
+        }
     }
 }