First, the word translated transparent is diaphanes and its used just once in the New Testament: here. It's a compound of dia ("through") and phaino ("shine"). If it's a bad translation, it's also a common one. From what I see, the only two English words translators use are "transparent" and "clear". Only the Aramaic Bible in Plain English avoids the word altogether:
And 12 gates and 12 pearls, one to each, and everyone of the gates was of one pearl, but the street of the city of pure gold, as if there was glass in it.
(By the way, this passage suggests the Greek, and not the Aramaic, New Testament was written first. It's easy to see how someone could make sense of "transparent gold" by saying that it's like gold with glass in it, but the other direction is unlikely.)
Strictly speaking, gold like clear glass isn't an oxymoron as there's nothing contradictory about transparent gold. We don't actually observe gold like this because when God made it in Genesis 1, He made it opaque. This is a new type of gold. Given the other descriptions of twelve exotic jewels decorating the New Jerusalem and the twelve gates made of single, giant pearls, the street of transparent gold isn't out of place.
Alternatively it's possible the passage intends us to understand the street to be fashioned by a master craftsman who is able to make glass out of gold the way glass makers use opaque ingredients like quartz sand to make transparent objects. Glass was difficult to make and very expensive in ancient times, so making glass out of gold would produce an exceedingly valuable material. In this sense, John may be following Job's struggle to value wisdom in Job 28:12-19 (ESV):
“But where shall wisdom be found?
And where is the place of understanding?
Man does not know its worth,
and it is not found in the land of the living.
The deep says, ‘It is not in me,’
and the sea says, ‘It is not with me.’
It cannot be bought for gold,
and silver cannot be weighed as its price.
It cannot be valued in the gold of Ophir,
in precious onyx or sapphire.
Gold and glass cannot equal it,
nor can it be exchanged for jewels of fine gold.
No mention shall be made of coral or of crystal;
the price of wisdom is above pearls.
The topaz of Ethiopia cannot equal it,
nor can it be valued in pure gold.
In Revelation, the extravagant language attempts to put a value on the new city. In the old Jerusalem (which would have been recently destroyed), the crowning glory was the temple of God. In the new city (which isn't heaven, but came from heaven to earth), the crowning glory is "the Lord God the Almighty and the Lamb." (Revelation 21:22b ESV) We aren't actually meant to put too much literal significance on the description of the city, but rather to use our imagination to conjure up a magnificence beyond what we have ever seen.