To deploy to App Engine, you’ll need to remove the <collapse-all-properties/> element from appengine/src/com/google/appinventor/YaClient.gwt.xml. With this in place, it builds one massive code base to distribute. When you remove it, it builds a variant per language and per browser so that the individual files are smaller at the expense of longer build times.
Edit: At MIT, we also turn on optimizations in both the blocklyeditor and appengine. To turn on optimizations in blocklyeditor, edit ploverConfig.js and change the mode from “RAW” to “SIMPLE”. To turn on optimizations in appengine, edit appengine/build.xml and change the line that includes “-style pretty” by replacing “-style pretty” with “-optimize 9”. Optionally, if you have a beefier machine you can specify the number of parallel threads used to speed up compilation by specifiying “-localWorkers N”, replacing N with the number of threads you’d like to use. This further reduces the size of the build and increases compile time (except the parallelization part).