It looks like you are pasting in something in a character set that is not recognised by the system.
You might be able to make it work by installing extra fonts on the server, but that only works in some cases.
Sorry, I should have pointed at this in the answer - https://confluence.atlassian.com/jirakb/jira-ui-shows-unreadable-text-on-captcha-and-some-gadgets-due-to-missing-fonts-941590036.html
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