From int languageId to string culture

src/Umbraco.Core/Collections/CompositeStringStringKey.cs

@@ -0,0 +1,41 @@
+using System;
+
+namespace Umbraco.Core.Collections
+{
+    /// <summary>
+    /// Represents a composite key of (string, string) for fast dictionaries.
+    /// </summary>
+    /// <remarks>
+    /// <para>The string parts of the key are case-insensitive.</para>
+    /// <para>Null is a valid value for both parts.</para>
+    /// </remarks>
+    public struct CompositeStringStringKey : IEquatable<CompositeStringStringKey>
+    {
+        private readonly string _key1;
+        private readonly string _key2;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="CompositeStringStringKey"/> struct.
+        /// </summary>
+        public CompositeStringStringKey(string key1, string key2)
+        {
+            _key1 = key1?.ToLowerInvariant() ?? "NULL";
+            _key2 = key2?.ToLowerInvariant() ?? "NULL";
+        }
+
+        public bool Equals(CompositeStringStringKey other)
+            => _key2 == other._key2 && _key1 == other._key1;
+
+        public override bool Equals(object obj)
+            => obj is CompositeStringStringKey other && _key2 == other._key2 && _key1 == other._key1;
+
+        public override int GetHashCode()
+            => _key2.GetHashCode() * 31 + _key1.GetHashCode();
+
+        public static bool operator ==(CompositeStringStringKey key1, CompositeStringStringKey key2)
+            => key1._key2 == key2._key2 && key1._key1 == key2._key1;
+
+        public static bool operator !=(CompositeStringStringKey key1, CompositeStringStringKey key2)
+            => key1._key2 != key2._key2 || key1._key1 != key2._key1;
+    }
+}