The letter ‘K’ as a mark of origin?

[Petrasti]

This is less about transliteration in EVA and more about what we recognize as "K" k and not "C". If a German speaker were to write a cipher or an unknown language phonetically, K would be dominant in German, since C is rare. But what would Spaniards or Italians in the Romance languages do? That's the question I'm asking. If K is recognized by us as K and also transliterated as k in EVA, in which linguistic area were these writers active if K is the dominant letter?