In English, we use Abitur and baccalauréat and everyone immediately knows what is at issue. I think Matura has also gained traction in recent years. In a long-winded report I would stick to Matura/maturita, the question is whether this is suitable for the translation of a simple certificate. Mind you, I also translate gymnnázium, where possible, as, well, gymnnázium or Gymnasium (not grammar school).

“Much like British A-levels or European Matura, the baccalauréat allows French and international students to obtain a standardised qualification, typically at the age of 18. “
http://en.wikipedia.org/wiki/Baccalauréat

“In the Slovak Republic, gymnázium is one type of schools that provide secondary education… All of them lead to the maturita exam.”
http://en.wikipedia.org/wiki/Gymnasium_(school)

To avoid country-specific terms, you could use the generic “high school graduation certificate” or “school-leaving certificate”

“Equivalent high school graduation certificate in other countries”
http://en.wikipedia.org/wiki/Abitur

“It is the only school-leaving certificate in all states of Germany that…”
http://en.wikipedia.org/wiki/Abitur

If the client wants a country-specific translation as per the other answers proposed, I wouldn’t demur.


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Note added at 3 hrs (2014-08-18 03:04:54 GMT)
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From the Oxford University admissions page:
“Slovakian Maturitńa Skúška/Maturita with výborný (excellent) in the majority of subjects.”
http://www.ox.ac.uk/admissions/undergraduate/international-s...