When did Good Friday first get called “Good”?
To be honest, we do not know for sure, but then possibly in 1290 if you accept "guode friday" as meaning Good Friday!
We honestly don’t know. Linguists are unable to trace when and where and why Crucifixion Day came to be known as Good Friday. The word “good” is sometimes used in the Bible in the sense of “holy.” So the term Good Friday might be derived from some olden expression such as Holy Friday. The word good may also relate in its etymology to the word God. Our term goodbye is apparently a contraction of the phrase God Be With You. Perhaps Good Friday hails from a medieval phrase meaning God’s Friday. - Why Is Good Friday Called Good Friday?
There are still some other possibilities of where this phrase may have originated, but as to when the term Good Friday was first used is somewhat mysterious.
There are two possible origins for the name "Good Friday". The first may have come from the Gallican Church in Gaul (modern-day France and Germany). The name "Gute Freitag" is Germanic in origin and literally means "good" or "holy" Friday. The second possibility is a variation on the name "God's Friday," where the word "good" was used to replace the word "God," which was often viewed as too holy to be spoken aloud. - Good Friday Origins
The following article has this to say about why Good Friday is Good?
The origin of the term Good is not clear. Some say it is from "God's Friday" (Gottes Freitag); others maintain that it is from the German Gute Freitag, and not specially English. Sometimes, too, the day was called Long Friday by the Anglo-Saxons; so today in Denmark.
If Good Friday were called good because English adopted the German phrase, then we would expect Gute Freitag to be the common German name for Good Friday, but it is not. Instead, Germans refer to Good Friday as Karfreitag—that is, Sorrowful or Suffering Friday—in German.
So, in the end, the historical origins of why Good Friday is called Good Friday remain unclear, but the theological reason is very likely the one expressed by the Baltimore Catechism: Good Friday is good because the death of Christ, as terrible as it was, led to the Resurrection on Easter Sunday, which brought new life to those who believe.
When did Good in Good Friday become used as an expression? Magazine Monitor states the following:
The earliest known use of "guode friday" is found in The South English Legendary, a text from around 1290, according to the dictionary.