l10n: Update translations from Weblate, except skip zh_Hans

Cherry-picked from 5466452, which
was in the v0.0.29 preview beta.  The cherry-pick required fixup
only in rerunning `tools/check l10n --fix`, which changed the set
of English fallback strings included in the new `de` translation.

This update required adjustment; straight from the Weblate branch,
l10n generation (`tools/check l10n --fix`) failed:

    Arb file for a fallback, zh, does not exist, even though
    the following locale(s) exist: [zh_Hans].
    When locales specify a script code or country code, a
    base locale (without the script code or country code) should
    exist as the fallback. Please create a {fileName}_zh.arb
    file.

The app_zh_Hans.arb file had only two translations in it; it exists
at the moment precisely in order to test this sort of workflow.
For the release, I just removed it and reran generation.
(We'll include it properly in a future change.)

Author: gnprice

assets/l10n/app_de.arb

@@ -0,0 +1 @@
+{}

assets/l10n/app_en_GB.arb

@@ -0,0 +1,6 @@
+{
+  "topicValidationErrorMandatoryButEmpty": "Topics are required in this organisation.",
+  "@topicValidationErrorMandatoryButEmpty": {
+    "description": "Topic validation error when topic is required but was empty."
+  }
+}

assets/l10n/app_pl.arb

@@ -1006,5 +1006,15 @@
         "example": "4.0"
       }
     }
+  },
+  "composeBoxEnterTopicOrSkipHintText": "Wpisz tytuł wątku (pomiń aby uzyskać “{defaultTopicName}”)",
+  "@composeBoxEnterTopicOrSkipHintText": {
+    "description": "Hint text for topic input widget in compose box when topics are optional.",
+    "placeholders": {
+      "defaultTopicName": {
+        "type": "String",
+        "example": "general chat"
+      }
+    }
   }
 }

assets/l10n/app_uk.arb

@@ -7,7 +7,7 @@
   "@actionSheetOptionFollowTopic": {
     "description": "Label for following a topic on action sheet."
   },
-  "actionSheetOptionUnstarMessage": "Зняти позначку зірочки з повідомлення",
+  "actionSheetOptionUnstarMessage": "Зняти позначку зірки з повідомлення",
   "@actionSheetOptionUnstarMessage": {
     "description": "Label for unstar button on action sheet."
   },
@@ -51,11 +51,11 @@
   "@errorSharingFailed": {
     "description": "Error message when sharing a message failed."
   },
-  "errorStarMessageFailedTitle": "Не вдалося позначити повідомлення зірочкою",
+  "errorStarMessageFailedTitle": "Не вдалося позначити повідомлення зіркою",
   "@errorStarMessageFailedTitle": {
     "description": "Error title when starring a message failed."
   },
-  "errorUnstarMessageFailedTitle": "Не вдалося зняти позначку зірочки з повідомлення",
+  "errorUnstarMessageFailedTitle": "Не вдалося зняти позначку зірки з повідомлення",
   "@errorUnstarMessageFailedTitle": {
     "description": "Error title when unstarring a message failed."
   },
@@ -157,7 +157,7 @@
   "@permissionsDeniedReadExternalStorage": {
     "description": "Message for dialog asking the user to grant permissions for external storage read access."
   },
-  "actionSheetOptionStarMessage": "Позначити повідомлення зірочкою",
+  "actionSheetOptionStarMessage": "Вибрати повідомлення",
   "@actionSheetOptionStarMessage": {
     "description": "Label for star button on action sheet."
   },
@@ -315,7 +315,7 @@
       }
     }
   },
-  "composeBoxGroupDmContentHint": "Група повідомлень",
+  "composeBoxGroupDmContentHint": "Написати групі",
   "@composeBoxGroupDmContentHint": {
     "description": "Hint text for content input when sending a message to a group."
   },
@@ -691,7 +691,7 @@
   "@mentionsPageTitle": {
     "description": "Page title for the 'Mentions' message view."
   },
-  "starredMessagesPageTitle": "Повідомлення, позначені зірочкою",
+  "starredMessagesPageTitle": "Вибрані повідомлення",
   "@starredMessagesPageTitle": {
     "description": "Page title for the 'Starred messages' message view."
   },
@@ -955,7 +955,7 @@
   "@recentDmConversationsPageTitle": {
     "description": "Title for the page with a list of DM conversations."
   },
-  "combinedFeedPageTitle": "Комбінована стрічка",
+  "combinedFeedPageTitle": "Об'єднана стрічка",
   "@combinedFeedPageTitle": {
     "description": "Page title for the 'Combined feed' message view."
   },

lib/generated/l10n/zulip_localizations.dart

@@ -6,6 +6,7 @@ import 'package:flutter_localizations/flutter_localizations.dart';
 import 'package:intl/intl.dart' as intl;
 
 import 'zulip_localizations_ar.dart';
+import 'zulip_localizations_de.dart';
 import 'zulip_localizations_en.dart';
 import 'zulip_localizations_ja.dart';
 import 'zulip_localizations_nb.dart';
@@ -102,6 +103,8 @@ abstract class ZulipLocalizations {
   static const List<Locale> supportedLocales = <Locale>[
     Locale('en'),
     Locale('ar'),
+    Locale('de'),
+    Locale('en', 'GB'),
     Locale('ja'),
     Locale('nb'),
     Locale('pl'),
@@ -1409,6 +1412,7 @@ class _ZulipLocalizationsDelegate
   @override
   bool isSupported(Locale locale) => <String>[
     'ar',
+    'de',
     'en',
     'ja',
     'nb',
@@ -1423,10 +1427,24 @@ class _ZulipLocalizationsDelegate
 }
 
 ZulipLocalizations lookupZulipLocalizations(Locale locale) {
+  // Lookup logic when language+country codes are specified.
+  switch (locale.languageCode) {
+    case 'en':
+      {
+        switch (locale.countryCode) {
+          case 'GB':
+            return ZulipLocalizationsEnGb();
+        }
+        break;
+      }
+  }
+
   // Lookup logic when only language code is specified.
   switch (locale.languageCode) {
     case 'ar':
       return ZulipLocalizationsAr();
+    case 'de':
+      return ZulipLocalizationsDe();
     case 'en':
       return ZulipLocalizationsEn();
     case 'ja':