Index: lldb/include/lldb/Target/Process.h
===================================================================
--- lldb/include/lldb/Target/Process.h
+++ lldb/include/lldb/Target/Process.h
@@ -86,6 +86,7 @@
   bool GetDetachKeepsStopped() const;
   void SetDetachKeepsStopped(bool keep_stopped);
   bool GetWarningsOptimization() const;
+  bool GetWarningsUnsupportedLanguage() const;
   bool GetStopOnExec() const;
   std::chrono::seconds GetUtilityExpressionTimeout() const;
   bool GetOSPluginReportsAllThreads() const;
@@ -390,7 +391,7 @@
   };
 
   /// Process warning types.
-  enum Warnings { eWarningsOptimization = 1 };
+  enum Warnings { eWarningsOptimization = 1, eWarningsUnsupportedLanguage = 2 };
 
   typedef Range<lldb::addr_t, lldb::addr_t> LoadRange;
   // We use a read/write lock to allow on or more clients to access the process
@@ -1319,6 +1320,12 @@
   ///     pre-computed.
   void PrintWarningOptimization(const SymbolContext &sc);
 
+  /// Print a user-visible warning about a function written in a
+  /// language that this version of LLDB doesn't support.
+  ///
+  /// \see PrintWarningOptimization
+  void PrintWarningUnsupportedLanguage(const SymbolContext &sc);
+
   virtual bool GetProcessInfo(ProcessInstanceInfo &info);
 
 public:
Index: lldb/source/Target/Process.cpp
===================================================================
--- lldb/source/Target/Process.cpp
+++ lldb/source/Target/Process.cpp
@@ -258,6 +258,12 @@
       nullptr, idx, g_process_properties[idx].default_uint_value != 0);
 }
 
+bool ProcessProperties::GetWarningsUnsupportedLanguage() const {
+  const uint32_t idx = ePropertyWarningUnsupportedLanguage;
+  return m_collection_sp->GetPropertyAtIndexAsBoolean(
+      nullptr, idx, g_process_properties[idx].default_uint_value != 0);
+}
+
 bool ProcessProperties::GetStopOnExec() const {
   const uint32_t idx = ePropertyStopOnExec;
   return m_collection_sp->GetPropertyAtIndexAsBoolean(
@@ -5761,9 +5767,6 @@
   StreamSP stream_sp = GetTarget().GetDebugger().GetAsyncOutputStream();
   if (!stream_sp)
     return;
-  if (warning_type == eWarningsOptimization && !GetWarningsOptimization()) {
-    return;
-  }
 
   if (repeat_key != nullptr) {
     WarningsCollection::iterator it = m_warnings_issued.find(warning_type);
@@ -5788,8 +5791,11 @@
 }
 
 void Process::PrintWarningOptimization(const SymbolContext &sc) {
-  if (GetWarningsOptimization() && sc.module_sp &&
-      !sc.module_sp->GetFileSpec().GetFilename().IsEmpty() && sc.function &&
+  if (!GetWarningsOptimization())
+    return;
+  if (!sc.module_sp)
+    return;
+  if (!sc.module_sp->GetFileSpec().GetFilename().IsEmpty() && sc.function &&
       sc.function->GetIsOptimized()) {
     PrintWarning(Process::Warnings::eWarningsOptimization, sc.module_sp.get(),
                  "%s was compiled with optimization - stepping may behave "
@@ -5798,6 +5804,25 @@
   }
 }
 
+void Process::PrintWarningUnsupportedLanguage(const SymbolContext &sc) {
+  if (!GetWarningsUnsupportedLanguage())
+    return;
+  if (!sc.module_sp)
+    return;
+  LanguageType language = sc.GetLanguage();
+  if (language == eLanguageTypeUnknown)
+    return;
+  auto type_system_or_err = sc.module_sp->GetTypeSystemForLanguage(language);
+  if (auto err = type_system_or_err.takeError()) {
+    llvm::consumeError(std::move(err));
+    PrintWarning(Process::Warnings::eWarningsUnsupportedLanguage,
+                 sc.module_sp.get(),
+                 "This version of LLDB has no plugin for the %s language. "
+                 "Inspection of frame variables will be limited.\n",
+                 Language::GetNameForLanguageType(language));
+  }
+}
+
 bool Process::GetProcessInfo(ProcessInstanceInfo &info) {
   info.Clear();
 
Index: lldb/source/Target/TargetProperties.td
===================================================================
--- lldb/source/Target/TargetProperties.td
+++ lldb/source/Target/TargetProperties.td
@@ -204,6 +204,9 @@
   def WarningOptimization: Property<"optimization-warnings", "Boolean">,
     DefaultTrue,
     Desc<"If true, warn when stopped in code that is optimized where stepping and variable availability may not behave as expected.">;
+  def WarningUnsupportedLanguage: Property<"unsupported-language-warnings", "Boolean">,
+    DefaultTrue,
+    Desc<"If true, warn when stopped in code that is written in a source language that LLDB does not support.">;
   def StopOnExec: Property<"stop-on-exec", "Boolean">,
     Global,
     DefaultTrue,
Index: lldb/source/Target/Thread.cpp
===================================================================
--- lldb/source/Target/Thread.cpp
+++ lldb/source/Target/Thread.cpp
@@ -326,10 +326,13 @@
   if (!frame)
     return;
 
-  if (frame->HasDebugInformation() && GetProcess()->GetWarningsOptimization()) {
+  if (frame->HasDebugInformation() &&
+      (GetProcess()->GetWarningsOptimization() ||
+       GetProcess()->GetWarningsUnsupportedLanguage())) {
     SymbolContext sc =
         frame->GetSymbolContext(eSymbolContextFunction | eSymbolContextModule);
     GetProcess()->PrintWarningOptimization(sc);
+    GetProcess()->PrintWarningUnsupportedLanguage(sc);
   }
 }
 
Index: lldb/test/Shell/Process/Inputs/true.c
===================================================================
--- /dev/null
+++ lldb/test/Shell/Process/Inputs/true.c
@@ -0,0 +1,3 @@
+int main(int argc, char **argv) {
+  return 0;
+}
Index: lldb/test/Shell/Process/Optimization.test
===================================================================
--- /dev/null
+++ lldb/test/Shell/Process/Optimization.test
@@ -0,0 +1,6 @@
+Test warnings.
+REQUIRES: shell
+RUN: %clang_host -O3 %S/Inputs/true.c -std=c99 -g -o %t.exe
+RUN: %lldb -o "b main" -o r -o q -b %t.exe | FileCheck %s
+
+CHECK: compiled with optimization
Index: lldb/test/Shell/Process/UnsupportedLanguage.test
===================================================================
--- /dev/null
+++ lldb/test/Shell/Process/UnsupportedLanguage.test
@@ -0,0 +1,8 @@
+Test warnings.
+REQUIRES: shell
+RUN: %clang_host %S/Inputs/true.c -std=c99 -g -c -S -emit-llvm -o - \
+RUN:   | sed -e 's/DW_LANG_C99/DW_LANG_PLI/g' >%t.ll
+RUN: %clang_host %t.ll -g -o %t.exe
+RUN: %lldb -o "b main" -o r -o q -b %t.exe | FileCheck %s
+
+CHECK: This version of LLDB has no plugin for the pli language