Emptiness and Nothingness.
Now lets dissect the definition:
- 从因缘生 -- 因 is the inner reason, 缘 is the outer reason, the two combined together, meaning the Ultimate Reason, is the cause of everything. Hence 一切事物从因缘生. You might want to think of it as dialectic reasoning, and you can do that.
- 唯心所造 says that everything is created by the Heart, the thinking device. It's idealism stripped to the bone.
- 自性 is the quality or essence of existence itself, since everything is caused by Reason and created by Heart, their Essence is null. Simply put, they don't Exist, hence 了无自性.
Even with a worldview like this, Buddhists still hold the Great Compassion, hence 观於空无而不舍大悲。
Then you ask what is Reason, what is Heart, and what is the Essence of Existence. The Buddha picks up a flower and smiles, and suddenly you reach Enlightenment.
Or you don't, in fact it's one of Buddha's disciples that does. I have friends struggling with these for decades, but still haven't reached anything remarkable, and I daresay, it's a complete waste of time.
As for translation, it depends on what you are translating. If you translate Buddhism classic texts, it's better to use Sanskrit words. If you translate a novel, or some random article with Buddhism references, use the capital like I did, or like Roger Zelazny did in his novel Lord of Light. It's a great book by the way.