Translate en.json in sr (#1440)

89% of minimum 80% translated source file: 'en.json'
on 'sr'.

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

Co-authored-by: transifex-integration[bot] <43880903+transifex-integration[bot]@users.noreply.github.com>
Co-authored-by: Anna Iosif <[email protected]>

Author: transifex-integration[bot]