There are only 2 language modes, not 3

src/runtime/runtime.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_RUNTIME_RUNTIME_H_
 #define V8_RUNTIME_RUNTIME_H_
 
 #include <memory>
 
 #include "src/allocation.h"
@@ skipping 1116 matching lines @@
 std::ostream& operator<<(std::ostream&, Runtime::FunctionId);
 
 //---------------------------------------------------------------------------
 // Constants used by interface to runtime functions.
 
 class AllocateDoubleAlignFlag : public BitField<bool, 0, 1> {};
 class AllocateTargetSpace : public BitField<AllocationSpace, 1, 3> {};
 
 class DeclareGlobalsEvalFlag : public BitField<bool, 0, 1> {};
 class DeclareGlobalsNativeFlag : public BitField<bool, 1, 1> {};
-STATIC_ASSERT(LANGUAGE_END == 3);
-class DeclareGlobalsLanguageMode : public BitField<LanguageMode, 2, 2> {};
+STATIC_ASSERT(LANGUAGE_END == 2);
+class DeclareGlobalsLanguageMode : public BitField<LanguageMode, 2, 1> {};
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_RUNTIME_RUNTIME_H_