Fix: conflicting strings issue in translations (#917)

* Fix conflicting strings issue in translations

* Preserve structure of `customTranslations`

* Use `deepmerge` to merge whole of `localized-strings`

* Simplify and make deep property access on an object safe

* Fix deep property accessor and rename it to idx

lib/core/utils.js

@@ -28,9 +28,14 @@ function getPath(pathStr, cleanUrl = false) {
     : removeExtension(pathStr);
 }
 
+function idx(target, path) {
+  return path.reduce((obj, key) => obj && obj[key], target);
+}
+
 module.exports = {
   blogPostHasTruncateMarker,
   extractBlogPostBeforeTruncate,
   getPath,
   removeExtension,
+  idx,
 };