Interaction between overrides and translations in Pyramid

main.py

from pyramid.config import Configurator

if __name__ == '__main__':
    config = Configurator()
    config.override_asset('app', 'app.subapp:app-overrides/')
    config.commit()
    config.add_translation_dirs('app:locale')

output

Traceback (most recent call last):
  File "/home/piotr/apps/pycharm-4.5.3/helpers/pydev/pydev_run_in_console.py", line 69, in <module>
    globals = run_file(file, None, None)
  File "/home/piotr/apps/pycharm-4.5.3/helpers/pydev/pydev_run_in_console.py", line 29, in run_file
    pydev_imports.execfile(file, globals, locals)  # execute the script
  File "/home/piotr/projects/pyramid/app/main.py", line 8, in <module>
    config.add_translation_dirs('app:locale')
  File "/home/piotr/projects/pyramid/pyramid/util.py", line 570, in wrapper
    result = wrapped(self, *arg, **kw)
  File "/home/piotr/projects/pyramid/pyramid/config/i18n.py", line 87, in add_translation_dirs
    directory)
pyramid.exceptions.ConfigurationError: "/home/piotr/projects/pyramid/app/locale" is not a directory

tree

app
├── __init__.py
├── main.py
└── subapp
    ├── app-overrides
    ├── __init__.py