Add implementation for LanguageCode class

src/WebExtensions.Net/Extensions/I18n/LanguageCode.cs

@@ -0,0 +1,25 @@
+using System.Text.Json.Serialization;
+
+namespace WebExtensions.Net.I18n
+{
+    [JsonConverter(typeof(MultiTypeJsonConverter<LanguageCode>))]
+    public partial class LanguageCode : BaseMultiTypeObject
+    {
+        private readonly string valueString;
+
+        /// <summary>Creates a new instance of <see cref="LanguageCode" />.</summary>
+        /// <param name="value">The value.</param>
+        public LanguageCode(string value) : base(value, typeof(string))
+        {
+            valueString = value;
+        }
+
+        /// <summary>Converts from <see cref="LanguageCode" /> to <see cref="string" />.</summary>
+        /// <param name="value">The value to convert from.</param>
+        public static implicit operator string(LanguageCode value) => value.valueString;
+
+        /// <summary>Converts from <see cref="string" /> to <see cref="LanguageCode" />.</summary>
+        /// <param name="value">The value to convert from.</param>
+        public static implicit operator LanguageCode(string value) => new(value);
+    }
+}