"The lunch is over."
Translation:Tá an lón thart.
I still think 'críochnaithe' would be better. 'Thart' works, but it seems to mean 'past' or 'gone', but there is an example in this link that works just like the question. 'Tá an cith thart' means 'the shower is over', so I guess the Duolingo translation is OK. https://www.teanglann.ie/ga/fgb/thart