There are only 2 language modes, not 3

src/globals.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_GLOBALS_H_
 #define V8_GLOBALS_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 254 matching lines @@
 // (sorted alphabetically)
 
 class FreeStoreAllocationPolicy;
 template <typename T, class P = FreeStoreAllocationPolicy> class List;
 
 // -----------------------------------------------------------------------------
 // Declarations for use in both the preparser and the rest of V8.
 
 // The Strict Mode (ECMA-262 5th edition, 4.2.2).
 
-enum LanguageMode { SLOPPY, STRICT, LANGUAGE_END = 3 };
-
+enum LanguageMode : uint32_t { SLOPPY, STRICT, LANGUAGE_END };
 
 inline std::ostream& operator<<(std::ostream& os, const LanguageMode& mode) {
   switch (mode) {
     case SLOPPY: return os << "sloppy";
     case STRICT: return os << "strict";
     default: UNREACHABLE();
   }
   return os;
 }
 
@@ skipping 869 matching lines @@
  public:
   enum { kNone = 0x00, kSignedSmall = 0x01, kNumber = 0x3, kAny = 0x7 };
 };
 
 }  // namespace internal
 }  // namespace v8
 
 namespace i = v8::internal;
 
 #endif  // V8_GLOBALS_H_