From @marianamirandapessoa
I've realised why Brest, Belarus was not generated: the cities dict in create_city_networks_from_pbf is using just the name of the city as a key.
This means there is only one entry for a city named "Brest" and in this case it is the French one, because it's positioned after the Berarusian one in the csv.
From @marianamirandapessoa