Added the informal address to the BeyondFacts Lab (#1176)

app/Tests/Tools/PluginSystem/FakeLanguagePlugin.cs

@@ -0,0 +1,33 @@
+using AIStudio.Tools.PluginSystem;
+
+namespace AIStudio.Tests.Tools.PluginSystem;
+
+/// <summary>
+/// A language plugin with texts of its own and a base language behind it, as PluginLanguage has.
+/// </summary>
+/// <param name="content">The texts of the language itself.</param>
+/// <param name="baseContent">The texts of the base language, which answer for the keys the language lacks.</param>
+public sealed class FakeLanguagePlugin(IReadOnlyDictionary<string, string> content, IReadOnlyDictionary<string, string>? baseContent = null) : ILanguagePlugin
+{
+    /// <inheritdoc />
+    public bool TryGetText(string key, out string value, bool logWarning = false)
+    {
+        if (content.TryGetValue(key, out var text) || baseContent is not null && baseContent.TryGetValue(key, out text))
+        {
+            value = text;
+            return true;
+        }
+
+        value = string.Empty;
+        return false;
+    }
+
+    /// <inheritdoc />
+    public string IETFTag => "de-DE";
+
+    /// <inheritdoc />
+    public string LangName => "Deutsch (Deutschland)";
+
+    /// <inheritdoc />
+    public IReadOnlyDictionary<string, string> Content => content;
+}