There are only 2 language modes, not 3

src/ast/scopes.cc

 // 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.
 
 #include "src/ast/scopes.h"
 
 #include <set>
 
 #include "src/accessors.h"
 #include "src/bootstrapper.h"
@@ skipping 70 matching lines @@
       variables_(zone),
       decls_(4, zone),
       scope_type_(scope_type) {
   SetDefaults();
   if (outer_scope == nullptr) {
     // If the outer scope is null, this cannot be a with scope. The outermost
     // scope must be a script scope.
     DCHECK_EQ(SCRIPT_SCOPE, scope_type);
   } else {
     asm_function_ = outer_scope_->asm_module_;
-    language_mode_ = outer_scope->language_mode_;
+    set_language_mode(outer_scope->language_mode());
     force_context_allocation_ =
         !is_function_scope() && outer_scope->has_forced_context_allocation();
     outer_scope_->AddInnerScope(this);
     scope_inside_with_ = outer_scope_->scope_inside_with_ || is_with_scope();
   }
 }
 
 Scope::Snapshot::Snapshot(Scope* scope)
     : outer_scope_(scope),
       top_inner_scope_(scope->inner_scope_),
@@ skipping 28 matching lines @@
       scope_info_(scope_info),
       scope_type_(scope_type) {
   SetDefaults();
 #ifdef DEBUG
   already_resolved_ = true;
 #endif
   if (scope_type == WITH_SCOPE) {
     DCHECK(scope_info.is_null());
   } else {
     scope_calls_eval_ = scope_info->CallsEval();
-    language_mode_ = scope_info->language_mode();
+    set_language_mode(scope_info->language_mode());
     num_heap_slots_ = scope_info->ContextLength();
   }
   DCHECK_LE(Context::MIN_CONTEXT_SLOTS, num_heap_slots_);
 
   if (inner_scope != nullptr) AddInnerScope(inner_scope);
 }
 
 DeclarationScope::DeclarationScope(Zone* zone, Scope* inner_scope,
                                    ScopeType scope_type,
                                    Handle<ScopeInfo> scope_info)
@@ skipping 46 matching lines @@
   unresolved_ = nullptr;
   dynamics_ = nullptr;
 
   start_position_ = kNoSourcePosition;
   end_position_ = kNoSourcePosition;
 
   num_stack_slots_ = 0;
   num_heap_slots_ = Context::MIN_CONTEXT_SLOTS;
   num_global_slots_ = 0;
 
-  language_mode_ = SLOPPY;
+  set_language_mode(SLOPPY);
 
   scope_inside_with_ = false;
   scope_calls_eval_ = false;
   scope_uses_super_property_ = false;
   has_arguments_parameter_ = false;
   asm_module_ = false;
   asm_function_ = false;
   scope_nonlinear_ = false;
   is_hidden_ = false;
   is_debug_evaluate_scope_ = false;
@@ skipping 780 matching lines @@
 
   // Push scope data up to migrate_to. Note that migrate_to and this Scope
   // describe the same Scope, just in different Zones.
   PropagateUsageFlagsToScope(migrate_to);
   if (inner_scope_calls_eval_) {
     migrate_to->inner_scope_calls_eval_ = true;
   }
   DCHECK(!force_eager_compilation_);
   migrate_to->set_start_position(start_position_);
   migrate_to->set_end_position(end_position_);
-  migrate_to->language_mode_ = language_mode_;
+  migrate_to->set_language_mode(language_mode());
   migrate_to->arity_ = arity_;
   migrate_to->force_context_allocation_ = force_context_allocation_;
   outer_scope_->RemoveInnerScope(this);
   DCHECK_EQ(outer_scope_, migrate_to->outer_scope_);
   DCHECK_EQ(outer_scope_->zone(), migrate_to->zone());
   DCHECK_EQ(NeedsHomeObject(), migrate_to->NeedsHomeObject());
   DCHECK_EQ(asm_function_, migrate_to->asm_function_);
   DCHECK_EQ(arguments() != nullptr, migrate_to->arguments() != nullptr);
 }
 
@@ skipping 759 matching lines @@
       function != nullptr && function->IsContextSlot();
   return num_heap_slots() - Context::MIN_CONTEXT_SLOTS - num_global_slots() -
          (is_function_var_in_context ? 1 : 0);
 }
 
 
 int Scope::ContextGlobalCount() const { return num_global_slots(); }
 
 }  // namespace internal
 }  // namespace v8