Flapper has some additional environment expectations.

content/ppapi_plugin/ppapi_plugin_main.cc

 // Copyright (c) 2012 The Chromium 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 "base/command_line.h"
 #include "base/debug/debugger.h"
 #include "base/i18n/rtl.h"
 #include "base/message_loop.h"
 #include "base/threading/platform_thread.h"
 #include "build/build_config.h"
 #include "content/common/child_process.h"
 #include "content/ppapi_plugin/ppapi_thread.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/common/main_function_params.h"
 #include "ppapi/proxy/proxy_module.h"
 #include "ui/base/ui_base_switches.h"
 
 #if defined(OS_WIN)
 #include "sandbox/win/src/sandbox.h"
 #endif
 
 #if defined(OS_LINUX)
 #include "content/public/common/sandbox_init.h"
 #endif
 
+#if defined(OS_POSIX) && !defined(OS_ANDROID)
+#include <stdlib.h>
+#endif
+
 #if defined(OS_WIN)
 sandbox::TargetServices* g_target_services = NULL;
 #else
 void* g_target_services = 0;
 #endif
 
 // Main function for starting the PPAPI plugin process.
 int PpapiPluginMain(const content::MainFunctionParams& parameters) {
   const CommandLine& command_line = parameters.command_line;
 
@@ skipping 10 matching lines @@
     else
       ChildProcess::WaitForDebugger("Ppapi");
   }
 
   // Set the default locale to be the current UI language. WebKit uses ICU's
   // default locale for some font settings (especially switching between
   // Japanese and Chinese fonts for the same characters).
   if (command_line.HasSwitch(switches::kLang)) {
     std::string locale = command_line.GetSwitchValueASCII(switches::kLang);
     base::i18n::SetICUDefaultLocale(locale);
+
+#if defined(OS_POSIX) && !defined(OS_ANDROID)
+    // TODO(shess): Flash appears to have a POSIX locale dependency
+    // outside of the existing PPAPI ICU support.  Certain games hang
+    // while loading, and it seems related to datetime formatting.
+    // http://crbug.com/155396
+    // http://crbug.com/155671
+    //
+    // ICU can accept "en-US" or "en_US", but POSIX wants "en_US".
+    // TODO(shess): "en_US.UTF-8" might be even better.
+    std::replace(locale.begin(), locale.end(), '-', '_');
+    setlocale(LC_ALL, locale.c_str());
+    setenv("LANG", locale.c_str(), 0);
+#endif
   }
 
   MessageLoop main_message_loop;
   base::PlatformThread::SetName("CrPPAPIMain");
 
 #if defined(OS_LINUX)
   content::InitializeSandbox();
 #endif
 
   ChildProcess ppapi_process;
   ppapi_process.set_main_thread(
       new PpapiThread(parameters.command_line, false));  // Not a broker.
 
   main_message_loop.Run();
   return 0;
 }