Have tried getting Craft working on Google App Engine (GAE) using the GAE SDK and after defining CRAFT_STORAGE_PATH first up in the index.php, setting it to a Google Cloud Storage path eg. gs://craft-gae-storage/ I found I had to uncomment the workings of craft_ensureFolderIsReadable function in bootstrap.php so it didn't fail on the folder checks, but then it still dies with the error:
Fatal error: Class 'Craft\PhpMessageSource' not found in /Users/.../Craft-gae-HappyLager/craft/app/framework/YiiBase.php on line 213
I'm using the HappyLager demo combined with the Yii GAE codebase from https://github.com/poul-kg/yii-app-engine with a slightly modified base setup to try to get craft working: https://github.com/moldedjelly/craft-gae
craft/app/etc/i18n
?echo __FILE__;
orCraft::log(__FILE__, LogLevel::Info, true);
if you want it to go to Craft's log files.