Docs: Document JSON format changes

There won't be single format in the end as they differ at time when
creating new unit. This is now properly documented and changes from
previous situation is covered by the docs as well.

Fixes #2149

docs/formats.rst

@@ -746,6 +746,11 @@ JSON files
     Since Weblate 2.16 and with translate-toolkit at-least 2.2.4, nested
     structure JSON files are supported as well.
 
+.. versionchanged:: 4.3
+
+    The structure of JSON file is properly preserved even for complex
+    situations which were broken in prior releases.
+
 JSON format is used mostly for translating applications implemented in
 JavaScript.
 
@@ -771,13 +776,12 @@ Nested files are supported as well (see above for requirements), such a file can
 .. literalinclude:: ../weblate/trans/tests/data/cs-nested.json
     :language: json
 
-.. warning::
-
-   Weblate currently handles nested JSON by flattening the keys. This leads to
-   serializing issues when special chars such as ``.`` or ``[]`` are used in
-   the actual keys, because Weblate thinks it is indication of nesting.
+.. hint::
 
-   See <https://github.com/WeblateOrg/weblate/issues/2149>
+   The :guilabel:`JSON file` and :guilabel:`JSON nested structure file` can
+   both handle same type of files. The only difference between them is when
+   adding new strings. The nested variant tries to parse the key and insert the
+   new string into the matching structure.
 
 +-------------------------------------------------------------------+
 | Typical Weblate :ref:`component`                                  |