Steps to reproduce:

1. Run JIRA in UTF-8 encoding as mentioned here - Internationalisation and Encoding Troubleshooting
2. Create a webhook connection with other application, such as http://requestb.in
3. Create a new issue in JIRA with issue description - Test: čšžćđ

Expected result:

...
"description": "http://requestb.in/1aru5ky1\r\n\r\nbody\" : ...\"Test: čšžćđ\"",
...

Result in client site:

...
"description": "http://requestb.in/1aru5ky1\r\n\r\nbody\" : ...\"Test: ?????\"",
...