Currently the "object" in the Activity.content is not translatable because it uses Activity.generate_content uses model.object_type which is purposefully forced to English as it's used in the API.

This could be fixed by doing:

{
    "image": _("an image"),
    "comment": _("a comment"),
    etc...
}

This would allow it be translatable and get the correct article in English which is currently missing.

While looking at ActivityIntermediator, I noticed some bits.

The .set method could probably be rewritten a bit:

# We need to flush so that self.id is populated
self.type = key
Session.flush()

# First set self as activity
obj.activity = self.id
Session.commit()

And instead of checking values in .save use a validator. See ​http://docs.sqlalchemy.org/en/latest/orm/mapper_config.html#simple-validators

@validates('type')
def validate_type(self, key, value):
    assert value in self.TYPES
    return value

With #905 we now have the activities that can be created when the user does something on GMG. However there is a fixed TYPES dictionary which doesn't allow plugins to add their models as objects which take part in activites.

The way this could be changed is to have a ActivityTypes table which is this map. The current TYPES can be populated by the FOUNDATIONS system and plugins can add themsleves to this table.