Is there any difference between "pero" and "propiska"? I thought "pero" was more like a fountain pen.
Propiska is a colloquial name for kuličkové pero = ballpoint pen. Pero is any kind of pen but sometimes can indeed designate a fountain pen specifically.
Mockrát děkuji za vysvětlení :)
Is there any difference between "Write with a black or blue pen" and "Write with a black or a blue pen" for a possible Czech translation?
Well, you can try to distinguish "Pište černým nebo modrým perem." and "Pište černým perem nebo modrým perem.", but the difference is very small.
Then I kindly ask "Write with a black or a blue pen" to be added to the possible translations :)
Please report it, if you get this one "wrong" again. We can no longer update the list of accepted translations, so it may be a while before adding your suggestion will be considered.