language mapping when two of same lanuages

Documentation/ApiOverview/Localization/TranslationServer/Crowdin/Faq.rst

@@ -137,6 +137,31 @@ located in the extension root directory.
     `Crowdin configuration file <https://support.crowdin.com/configuration-file/>`__
 
 
+..  index:: Crowdin; language Mapping
+..  _crowdin-faq-language-mapping:
+
+Some files require your attention
+---------------------------------
+
+There is a message on top of your project in Crowdin telling that there is a problem
+with your files. If you follow the links you will most likely see your source files
+marked with red color and a hover text telling that the export pattern is wrong and
+translations will not be exported for the language that shares the same language code.
+
+In TYPO3 we use `%two_letters_code%` for language codes and for a few cases this is forbidden
+when you have two Chinese, French, Portuguese and similar languages. All of our languages are
+required to be exported with `%two_letters_code%` so we decided to keep using the mentioned placeholder.
+As for Chinese Simplified, French Canadian, Portuguese Brazilian and similar language variety or regional dialect,
+you have to set up “Language mapping” for them. It allows you to customize the language code be used on export.
+
+Here is a list of the most common `%two_letters_code%` you can use in the "Language Mapping" that you
+find under the Project's :guilabel:`Settings > Languages`:
+
+*   Chinese Simplified: `zh_CH`
+*   Chinese Traditional: `zh_HK`
+*   French Canadian: `fr_CA`
+*   Portuguese Brazilian: `pt_BR`
+
 ..  index:: Crowdin; Upload XLIFF files
 ..  _crowdin-faq-upload-xliff-files: