feat: Translate frontend/src/i18n/en.json in ru

93% of minimum 50% translated source file: 'frontend/src/i18n/en.json'
on 'ru'.

Sync of partially translated files: 
untranslated content is included with an empty translation 
or source language content depending on file format

frontend/src/i18n/ru.json

@@ -24,7 +24,7 @@
     "ok": "OK",
     "permalink": "Получить постоянную ссылку",
     "previous": "Назад",
-    "preview": "Preview",
+    "preview": "Предпросмотр",
     "publish": "Опубликовать",
     "rename": "Переименовать",
     "replace": "Перезаписать",