There are seven map sizes in 0 A.D.:
# tiny (2 × 64 = 128 tiles)
# small (3 × 64 = 192 tiles)
# medium (4 × 64 = 256 tiles); default
# normal (5 × 64 = 320 tiles)
# large (6 × 64 = 384 tiles)
# very large (7 × 64 = 448 tiles)
# giant (8 × 64 = 512 tiles)
Now from a linguistic point of view, it's a bit odd that the third option is called “medium” and the fourth “normal”.
The fourth option is both the mean and the median of all map sizes; therefore “Medium” would be the correct name ([[ https://www.lexico.com/definition/medium | medium ]] (adjective) means “About halfway between two extremes of size or another quality; average.”).
The third option is the default map size; therefore “Normal” would be the correct name ([[ https://www.lexico.com/definition/normal | normal ]] (adjective) means “Conforming to a standard; usual, typical, or expected.”).
This patch thus simply swaps the “Medium” and “Normal” names.