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

app/SharedTools/I18NAddressVariant.cs

@@ -0,0 +1,43 @@
+namespace SharedTools;
+
+/// <summary>
+/// Names the keys of the two variants of a text with TA(), which addresses the reader.
+/// </summary>
+/// <remarks>
+/// Many languages tell a formal address from an informal one, such as "Sie" and "du" in German. A text with TA()
+/// therefore has two keys: its usual key, whose translation addresses the reader formally like all texts of the
+/// app, and the same key with INFORMAL_SUFFIX, whose translation addresses the reader informally. The I18N
+/// collector writes both keys, and the app looks up the informal one when the person wants to be addressed so.
+/// </remarks>
+public static class I18NAddressVariant
+{
+    /// <summary>
+    /// The end of the key of the variant with the informal address.
+    /// </summary>
+    public const string INFORMAL_SUFFIX = "::INFORMAL";
+
+    /// <summary>
+    /// Gets the key of the variant with the informal address.
+    /// </summary>
+    /// <param name="key">The usual key of the text, which stands for the formal address.</param>
+    /// <returns>The key of the informal variant.</returns>
+    public static string InformalKeyOf(string key) => $"{key}{INFORMAL_SUFFIX}";
+
+    /// <summary>
+    /// Tries to get the usual key of a text from the key of its informal variant.
+    /// </summary>
+    /// <param name="key">Any key.</param>
+    /// <param name="formalKey">The usual key of the text, or the given key when it belongs to no informal variant.</param>
+    /// <returns>True, when the given key belongs to an informal variant.</returns>
+    public static bool TryGetFormalKey(string key, out string formalKey)
+    {
+        if (key.EndsWith(INFORMAL_SUFFIX, StringComparison.Ordinal))
+        {
+            formalKey = key[..^INFORMAL_SUFFIX.Length];
+            return true;
+        }
+
+        formalKey = key;
+        return false;
+    }
+}