Fix the exercise configure files output in container|i18n mounts

The submit directive used to ignore the multilingual
`container|i18n` setting when it added the mount directories to
the configure files setting in the build output YAML.

directives/abstract_exercise.py

@@ -1,4 +1,5 @@
 import itertools
+from typing import Any, Mapping
 from urllib.parse import urlparse
 
 from docutils.parsers.rst import Directive, directives
@@ -69,6 +70,20 @@ def set_assistant_permissions(self, data):
         if 'allow-assistant-viewing' in self.options:
             data['allow_assistant_viewing'] = str_to_bool(self.options['allow-assistant-viewing'])
 
+    def set_configure_files_from_container(
+            self,
+            configure_files: Mapping[str, str],
+            container: Mapping[str, Any],
+            ) -> None:
+        mount: str = container.get("mount")
+        mounts: dict = container.get("mounts")
+        if mount:
+            configure_files[mount] = mount
+        if mounts:
+            for path_in_repo, path_in_container in mounts.items():
+                configure_files[path_in_repo] = path_in_repo
+
+
 class ConfigurableExercise(AbstractExercise):
     option_spec = {
         'configure-url': directives.unchanged,

directives/submit.py

@@ -181,11 +181,11 @@ def run(self):
 
         configure_files = {}
         if "container" in data and isinstance(data["container"], dict):
-            if "mount" in data["container"]:
-                configure_files[data["container"]["mount"]] = data["container"]["mount"]
-            if "mounts" in data["container"]:
-                for path_in_repo, path_in_container in data["container"]["mounts"].items():
-                    configure_files[path_in_repo] = path_in_repo
+            self.set_configure_files_from_container(configure_files, data["container"])
+        elif "container|i18n" in data and isinstance(data["container|i18n"], dict):
+            for lang, lcontainer in data["container|i18n"].items():
+                self.set_configure_files_from_container(configure_files, lcontainer)
+
         if "template" in data:
             configure_files[data["template"]] = data["template"]
         if "feedback_template" in data: