sugestão

no Brasil

Apparently, the French system brings a secondary school, or a middle school, which has four years instead of three (the traditional three plus what is called 8th grade in Brazil).
Just see the link I have pasted here.
We should always try to copy the sound and shape of the original expression.
Notice that my link still refers to a school, not a university, so that I chose 'escola secundaria'.
I thought of saying College, but, in Brazil, Primary School is also inside of the Colegios at least sometimes, so that this is clearer.

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Note added at 6 days (2013-09-03 17:50:23 GMT)
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I actually refined the expression to 'diploma de escola secundaria do tipo frances' because I think that if we say Secondary School Diploma of the French Type we are actually saying it is not necessarily a French Diploma, but a Diploma in the French Style, which I think is more what we want, since they have it in the USA, for instance (link that I have posted to you). Oh, well, it all depends on the context. I am definitely a contextualist, so there we go: If the person got it in France, then the first option I gave you is the most adequate one. If the person got it outside of France, then the second option is the most adequate one, I suppose. I am willing to discuss this one, so you can write to me.