Add translations for simple_translation app

.tx/config

@@ -104,3 +104,8 @@ source_file = wagtail/contrib/table_block/locale/en/LC_MESSAGES/django.po
 source_lang = en
 type = PO
 
+[wagtail.wagtailsimpletranslation]
+file_filter = wagtail/contrib/simple_translation/locale/<lang>/LC_MESSAGES/django.po
+source_file = wagtail/contrib/simple_translation/locale/en/LC_MESSAGES/django.po
+source_lang = en
+type = PO

wagtail/contrib/simple_translation/locale/en/LC_MESSAGES/django.po

@@ -0,0 +1,75 @@
+# SOME DESCRIPTIVE TITLE.
+# Copyright (C) YEAR THE PACKAGE'S COPYRIGHT HOLDER
+# This file is distributed under the same license as the PACKAGE package.
+# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
+#
+#, fuzzy
+msgid ""
+msgstr ""
+"Project-Id-Version: PACKAGE VERSION\n"
+"Report-Msgid-Bugs-To: \n"
+"POT-Creation-Date: 2021-04-21 09:32+0100\n"
+"PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
+"Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
+"Language-Team: LANGUAGE <LL@li.org>\n"
+"Language: \n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+"Plural-Forms: nplurals=2; plural=(n != 1);\n"
+
+#: apps.py:8
+msgid "Wagtail simple translation"
+msgstr ""
+
+#: forms.py:10
+msgid "Select all"
+msgstr ""
+
+#: forms.py:12
+msgid "Locales"
+msgstr ""
+
+#: forms.py:17
+msgid "All child pages will be created."
+msgstr ""
+
+#: forms.py:31
+msgid "Include subtree ({} page)"
+msgid_plural "Include subtree ({} pages)"
+msgstr[0] ""
+msgstr[1] ""
+
+#: templates/simple_translation/admin/submit_translation.html:25
+msgid "Submit"
+msgstr ""
+
+#: tests/test_views.py:44 tests/test_views.py:45 views.py:21
+#: wagtail_hooks.py:55 wagtail_hooks.py:74
+msgid "Translate"
+msgstr ""
+
+#: views.py:73
+msgid "{} locales"
+msgstr ""
+
+#: views.py:91
+msgid "Translate page"
+msgstr ""
+
+#: views.py:110
+msgid "The page '{page_title}' was successfully created in {locales}"
+msgstr ""
+
+#: views.py:116
+msgid "Translate {model_name}"
+msgstr ""
+
+#: views.py:141
+msgid "Successfully created {locales} for {model_name} '{object}'"
+msgstr ""
+
+#: wagtail_hooks.py:76
+#, python-format
+msgid "Translate '%(title)s'"
+msgstr ""