Change XModule i18n to use runtime.service

LMS-1597

common/lib/xmodule/xmodule/capa_module.py

@@ -22,7 +22,6 @@ from xmodule.exceptions import NotFoundError, ProcessingError
 from xblock.fields import Scope, String, Boolean, Dict, Integer, Float
 from .fields import Timedelta, Date
 from django.utils.timezone import UTC
-from django.utils.translation import ugettext as _
 
 log = logging.getLogger("edx.courseware")
 
@@ -359,6 +358,7 @@ class CapaModule(CapaFields, XModule):
         """
         # The logic flow is a little odd so that _('xxx') strings can be found for
         # translation while also running _() just once for each string.
+        _ = self.runtime.service(self, "i18n").ugettext
         check = _('Check')
         final_check = _('Final Check')
 

common/lib/xmodule/xmodule/video_module.py

@@ -21,7 +21,6 @@ import copy
 
 from django.http import Http404
 from django.conf import settings
-from django.utils.translation import ugettext as _
 
 from xmodule.x_module import XModule
 from xmodule.editing_module import TabsEditingDescriptor
@@ -302,6 +301,7 @@ class VideoDescriptor(VideoFields, TabsEditingDescriptor, EmptyDataRawDescriptor
             else:
                 return ''
 
+        _ = self.runtime.service(self, "i18n").ugettext
         video_url.update({
             'help': _('A YouTube URL or a link to a file hosted anywhere on the web.'),
             'display_name': 'Video URL',

common/lib/xmodule/xmodule/x_module.py

@@ -362,6 +362,7 @@ descriptor_attr = partial(ProxyAttribute, 'descriptor')  # pylint: disable=inval
 module_runtime_attr = partial(ProxyAttribute, 'xmodule_runtime')  # pylint: disable=invalid-name
 
 
+@XBlock.needs("i18n")
 class XModule(XModuleMixin, HTMLSnippet, XBlock):  # pylint: disable=abstract-method
     """ Implements a generic learning module.
 
@@ -563,6 +564,7 @@ class ResourceTemplates(object):
             return None
 
 
+@XBlock.needs("i18n")
 class XModuleDescriptor(XModuleMixin, HTMLSnippet, ResourceTemplates, XBlock):
     """
     An XModuleDescriptor is a specification for an element of a course. This