Old English being used in the 5th century.
Firstusage of the word "reality" found in 15th century.
This being 21st century.
Old English is not 5th Century. It post dates the influx of the Angles and the Saxons, which began in the 5th Century but did not immediately exclude Celtic speaking peoples. The most common Fifth Century language would have been a Celtic variant or a Romano British version of Latin. Educated people would have understood both.
The development of Old English from a combination of Anglo Saxon and extant languages, and its spread across Britain, took many centuries. Examples of Old English that we have today depend on two factors; the spread of literacy during a period of relative stability and peace, and the change from writing purely in Latin to writing in Old English as well. They therefore post date Alfred the Great, who is rightly known as the Father of the English Language.
Meanwhile this might be the 21st century, but there are still plenty of people around who have studied, and who can read and understand Old English, as well as the Middle, Modern and New variants.
Meanwhile, the reason why 'reality' is first found in the 15th century is that this is when this particular word was first written down. We do not know how long before that it was used orally; it could have been ten years, or twenty, or just five minutes.
This does not mean that the Anglo Saxons did not have a concept of reality, or a word for it. I am pretty sure they did. In Latin the term used would be veritas, meaning truth. I don't imagine there is any language on earth that cannot distinguish between that which is true and that which is not, or that does not have words to enable them to do so.
Old English - Wikipedia, the free encyclopedia
You're right again. It all depends.
I'm sure it makes a difference if this is the real universe or "merely a copy" of the real one too.
In Christian terms, this is the real one, but it is certainly not all that exists. There is a lot of congruence with the thinking of Plato et al.