fix: allow Unicode letters as first character in identifiers (issue #416)

source/Handlebars.Test/IssueTests.cs

@@ -726,6 +726,20 @@ public void UnrecognisedExpressionThrowsOutOfMemoryException()
             Assert.Throws<HandlebarsCompilerException>(()=> Handlebars.Compile(source));
         }
 
+        // Issue: https://github.com/Handlebars-Net/Handlebars.Net/issues/416
+        // Non-ASCII characters not supported as the first character of a placeholder identifier
+        [Fact]
+        public void Issue416_UnicodeFirstCharacterInIdentifier()
+        {
+            var config = new HandlebarsConfiguration { TextEncoder = new HtmlEncoder() };
+            var handlebars = Handlebars.Create(config);
+            // Japanese characters as identifiers — first char is non-ASCII
+            var template = handlebars.Compile("Hello {{姓}} {{名}},");
+            var data = new Dictionary<string, object> { { "姓", "山田" }, { "名", "太郎" } };
+            var result = template(data);
+            Assert.Equal("Hello 山田 太郎,", result);
+        }
+
         // Issue: https://github.com/Handlebars-Net/Handlebars.Net/issues/545
         // Partial registered on an instance should be found during render on that same instance
         [Fact]

source/Handlebars/Compiler/Lexer/Parsers/WordParser.cs

@@ -45,7 +45,9 @@ public override Token Parse(ExtendedStringReader reader)
         private static bool IsWord(ExtendedStringReader reader)
         {
             var peek = reader.Peek();
-            return ValidWordStartCharacters.Contains((char) peek);
+            if (peek == -1) return false;
+            var c = (char) peek;
+            return ValidWordStartCharacters.Contains(c) || char.IsLetter(c);
         }
 
         private static string AccumulateWord(ExtendedStringReader reader)