Looks like those language strings are programmatically generated so our language parser didn't pick them up. Using the language overrides feature within your language plugin try the following.
Key: unpaid
Text: unpaid-TRANSLATED
You should be able to do the same for the following strings as well.
Pay Now
expired
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cancelled
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Have added a bug ticket to add phpdoc for those language strings so our language parser will properly package them in the language plugin.
forge.joomlapolis.com/issues/7673
See the below if unsure how to use language overrides.
www.joomlapolis.com/blog/kyle/18701-language-overrides-have-arrived