diff --git a/lldb/include/lldb/Target/Language.h b/lldb/include/lldb/Target/Language.h
--- a/lldb/include/lldb/Target/Language.h
+++ b/lldb/include/lldb/Target/Language.h
@@ -279,6 +279,15 @@
   static void PrintAllLanguages(Stream &s, const char *prefix,
                                 const char *suffix);
 
+  /// Prints each language type that the current target supports
+  /// to the specified stream 's'.
+  ///
+  /// \param[out] s      Stream to which the language types are written.
+  /// \param[in]  prefix String that is prepended to the language type.
+  /// \param[in]  suffix String that is appended to the language type.
+  static void PrintSupportedLanguages(Stream &s, llvm::StringRef prefix,
+                                      llvm::StringRef suffix);
+
   // return false from callback to stop iterating
   static void ForAllLanguages(std::function<bool(lldb::LanguageType)> callback);
 
diff --git a/lldb/source/Commands/CommandObjectExpression.cpp b/lldb/source/Commands/CommandObjectExpression.cpp
--- a/lldb/source/Commands/CommandObjectExpression.cpp
+++ b/lldb/source/Commands/CommandObjectExpression.cpp
@@ -42,10 +42,15 @@
   switch (short_option) {
   case 'l':
     language = Language::GetLanguageTypeFromString(option_arg);
-    if (language == eLanguageTypeUnknown)
-      error.SetErrorStringWithFormat(
-          "unknown language type: '%s' for expression",
-          option_arg.str().c_str());
+    if (language == eLanguageTypeUnknown) {
+      StreamString sstr;
+      sstr.Printf("unknown language type: '%s' for expression. "
+                  "List of supported languages:\n",
+                  option_arg.str().c_str());
+
+      Language::PrintSupportedLanguages(sstr, "  ", "\n");
+      error.SetErrorString(sstr.GetString());
+    }
     break;
 
   case 'a': {
diff --git a/lldb/source/Target/Language.cpp b/lldb/source/Target/Language.cpp
--- a/lldb/source/Target/Language.cpp
+++ b/lldb/source/Target/Language.cpp
@@ -221,6 +221,16 @@
     return language_names[eLanguageTypeUnknown].name;
 }
 
+void Language::PrintSupportedLanguages(Stream &s, llvm::StringRef prefix,
+                                       llvm::StringRef suffix) {
+  auto supported = Language::GetSupportedLanguages();
+  for (auto const &lang : supported) {
+    s << prefix;
+    s << Language::GetNameForLanguageType(lang);
+    s << suffix;
+  }
+}
+
 void Language::PrintAllLanguages(Stream &s, const char *prefix,
                                  const char *suffix) {
   for (uint32_t i = 1; i < num_languages; i++) {
diff --git a/lldb/test/API/commands/expression/invalid-args/TestInvalidArgsExpression.py b/lldb/test/API/commands/expression/invalid-args/TestInvalidArgsExpression.py
--- a/lldb/test/API/commands/expression/invalid-args/TestInvalidArgsExpression.py
+++ b/lldb/test/API/commands/expression/invalid-args/TestInvalidArgsExpression.py
@@ -7,7 +7,9 @@
     @no_debug_info_test
     def test_invalid_lang(self):
         self.expect("expression -l foo --", error=True,
-                    substrs=["error: unknown language type: 'foo' for expression"])
+                    substrs=["error: unknown language type: 'foo' for expression",
+                             "List of supported languages:",
+                             "c++"])
 
     @no_debug_info_test
     def test_invalid_all_thread(self):