There are only 2 language modes, not 3

src/objects.h

 // Copyright 2015 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_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 #include <memory>
 
@@ skipping 4383 matching lines @@
              VariableLocation* location, InitializationFlag* init_flag,
              MaybeAssignedFlag* maybe_assigned_flag);
 
   // Used for the function name variable for named function expressions, and for
   // the receiver.
   enum VariableAllocationInfo { NONE, STACK, CONTEXT, UNUSED };
 
   // Properties of scopes.
   class ScopeTypeField : public BitField<ScopeType, 0, 4> {};
   class CallsEvalField : public BitField<bool, ScopeTypeField::kNext, 1> {};
-  STATIC_ASSERT(LANGUAGE_END == 3);
+  STATIC_ASSERT(LANGUAGE_END == 2);
   class LanguageModeField
-      : public BitField<LanguageMode, CallsEvalField::kNext, 2> {};
+      : public BitField<LanguageMode, CallsEvalField::kNext, 1> {};
   class DeclarationScopeField
       : public BitField<bool, LanguageModeField::kNext, 1> {};
   class ReceiverVariableField
       : public BitField<VariableAllocationInfo, DeclarationScopeField::kNext,
                         2> {};
   class HasNewTargetField
       : public BitField<bool, ReceiverVariableField::kNext, 1> {};
   class FunctionVariableField
       : public BitField<VariableAllocationInfo, HasNewTargetField::kNext, 2> {};
   class FunctionVariableMode
@@ skipping 3157 matching lines @@
     kIsSubclassConstructor,
     kIsBaseConstructor,
     kIsGetterFunction,
     kIsSetterFunction,
     // byte 3
     kIsAsyncFunction,
     kDeserialized,
     kIsDeclaration,
     kCompilerHintsCount,  // Pseudo entry
   };
-  // Add hints for other modes when they're added.
-  STATIC_ASSERT(LANGUAGE_END == 3);
   // kFunctionKind has to be byte-aligned
   STATIC_ASSERT((kFunctionKind % kBitsPerByte) == 0);
 // Make sure that FunctionKind and byte 2 are in sync:
 #define ASSERT_FUNCTION_KIND_ORDER(functionKind, compilerFunctionKind) \
   STATIC_ASSERT(FunctionKind::functionKind ==                          \
                 1 << (compilerFunctionKind - kFunctionKind))
   ASSERT_FUNCTION_KIND_ORDER(kArrowFunction, kIsArrow);
   ASSERT_FUNCTION_KIND_ORDER(kGeneratorFunction, kIsGenerator);
   ASSERT_FUNCTION_KIND_ORDER(kConciseMethod, kIsConciseMethod);
   ASSERT_FUNCTION_KIND_ORDER(kDefaultConstructor, kIsDefaultConstructor);
@@ skipping 3577 matching lines @@
     }
     return value;
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #endif  // V8_OBJECTS_H_