zh locale missing keys in msgstr

When trying to run: `django-admin compilemessages`

I get these messages:
```
/schedule/locale/zh/LC_MESSAGES/django.po:135: a format specification for argument 'title' doesn't exist in 'msgstr'
/schedule/locale/zh/LC_MESSAGES/django.po:172: a format specification for argument 'end' doesn't exist in 'msgstr'
```

Locale problem strings are:
```
#: occurrence.py:14
#, python-format
msgid "%(start)s to %(end)s"
msgstr "（开始）到（结束）"
```
and
```
#: models.py:310
#, python-format
msgid "%(title)s: %(start)s-%(end)s"
msgstr "月（开始-结束）: %(start)s-%(end)s"
```

Open schedule/locale/zh/LC_MESSAGES/django.po and inspect the entries around lines 135 and 172, comparing each msgstr with its msgid placeholders. Run django-admin compilemessages before and after the translation update; done means the zh catalog compiles without the reported format-specification errors.

Written by the indexing model from the issue text.