Since BE is apparently what's being requested here, this is now OT, but....
Q: I have a high school diploma in English, maths and German? oder wie würde ich das sagen?
A: Einem Amerikaner kannst du das so sagen, ein Brite würde das zwar wahrscheinlich erraten können, aber nicht unbedingt verstehen.
That wouldn't make much sense to folks in the US, either. First, we don't say "maths"--even though it is "mathematics," we say "math." It's also not normal to get a high-school diploma in any specific subject. They aren't listed that way. States/schools have their general requirements for all people, but you can usually design your course of studies as will best serve you later. If you want to go to college next, you typically have to take more English, math, foreign-language, and science courses, etc. If you're going into a trade, you can often take courses in that direction.
In BE, it's important to avoid "graduate". You only graduate from a university.
AE doesn't make that distinction. (But you do get a diploma from high school, not a degree.)