You can override the default locale(s) that will be built/run by passing a
locales option to mope build or mope run.
Example
$ mope build browser --locales es fr-FR de-DR
mope build uses NODE_ENV to determine the default locales to build. In dev,
it will default to building only en-US. In production, it will build all the
locales with declared support in the application's src/util/locales.js module.