When adding an attachment which filename contains non ASCII characters via REST API, the filename will not be properly stored and displayed in JIRA.

For an example, when adding an attachment with the filename ÉíüÄ.txt, then the filename in the issue will be rendered as "����.txt". Please see the following screenshot:

Steps to reproduce the behavior:

• Create a test file, and name the file using any non-ASCII characters
• Attach the file to a JIRA issue via REST. Sample command will be:

  curl -D- -u admin:admin -X POST -H "X-Atlassian-TOken: nocheck" -Q "OPTS UTF8 ON" -F "file=@ÉíüÄ.txt" http://localhost:8080/rest/api/2/issue/NP-1/attachments
  

• After adding the attachment, go back to the related issue and check the attached file name