A few improvements to extract.

Use the configuration more, and we don't need to delete files we're
about to create.

conf/locale/config.yaml

@@ -32,6 +32,15 @@ locales:
 # The locale used for fake-accented English, for testing.
 dummy-locale: eo
 
+# Directories we don't search for strings.
+ignore_dirs:
+    - docs
+    - src
+    - i18n
+    - test_root
+    - common/static/xmodule/modules
+    - common/static/xmodule/descriptors
+
 # How should .po files be segmented?  See i18n/segment.py for details. Strings
 # that are only found in a particular segment are segregated into that .po file
 # so that translators can focus on separate parts of the product.

i18n/extract.py

@@ -40,15 +40,13 @@ def main():
     create_dir_if_necessary(LOCALE_DIR)
     source_msgs_dir = CONFIGURATION.source_messages_dir
 
-    remove_file(source_msgs_dir.joinpath('django.po'))
-    generated_files = ('django-partial.po', 'djangojs.po', 'mako.po')
-    for filename in generated_files:
-        remove_file(source_msgs_dir.joinpath(filename))
+    generated_files = ['django-partial.po', 'djangojs.po', 'mako.po']
 
     # Prepare makemessages command.
-    ignore_dirs = ["docs", "src", "i18n", "test_root"]
-    ignores = " ".join("--ignore={}/*".format(d) for d in ignore_dirs)
-    makemessages = 'django-admin.py makemessages -l en ' + ignores
+    makemessages = "django-admin.py makemessages -l en"
+    ignores = " ".join("--ignore={}/*".format(d) for d in CONFIGURATION.ignore_dirs)
+    if ignores:
+        makemessages += " " + ignores
 
     # Extract strings from mako templates.
     babel_mako_cmd = 'pybabel extract -F %s -c "Translators:" . -o %s' % (BABEL_CONFIG, BABEL_OUT)
@@ -80,6 +78,7 @@ def main():
         strip_key_strings(po)
         po.save()
 
+
 def fix_header(po):
     """
     Replace default headers with edX headers