Thanks for the translation!
That still doesn't answer the question how the card updates the account balance. Do you regularly have to go to the commercial guild to present your guild card so they can update your account balance?
Because that was the part that I thought Meria would be interested in, the transactions between cards is just a short distance communication technology.
Also pretty interesting that the Guild card has seemingly two functions, a computer that identifys the owner and keeps track of the account balance and an automatic system that coverts sound to light and light to sound. The decrease in volume is due to the guild card radiating the light in all directions, thus only a small amount of the energy actually makes it to the other card, resulting in decreased intensity.
Also also, Maria's plan might run into problems due to interference, in a network of guild cards, anything that one card heard gets transmitted to all other cards, possibly resulting in feedback loops.