Add support for minting additional fiat currencies (GBP, CHF, etc.)

[slekrem]

Feature Request

Current State

Currently, cashu.me supports the following fiat currencies with cent-based amounts:

• USD (1.00 USD = 100 amount)
• EUR (1.00 EUR = 100 amount)

This is implemented in:

• src/stores/mints.ts:233-241 - activeUnitCurrencyMultiplyer getter
• src/stores/ui.ts:93-114 - formatCurrency function

Proposed Enhancement

Add support for additional fiat currencies that use similar cent-based denomination systems, such as:

• GBP (British Pound Sterling) - 1.00 GBP = 100 pence
• CHF (Swiss Franc) - 1.00 CHF = 100 rappen/centimes
• CAD (Canadian Dollar) - 1.00 CAD = 100 cents
• AUD (Australian Dollar) - 1.00 AUD = 100 cents
• JPY (Japanese Yen) - no subdivisions (multiplier = 1)
• And potentially others

Implementation Requirements

1. Update activeUnitCurrencyMultiplyer in src/stores/mints.ts to include new currencies
2. Update formatCurrency in src/stores/ui.ts to handle new currencies
3. Update unitTickerShortMap in src/stores/ui.ts for currency symbols/abbreviations
4. Update activeUnitLabel getter in src/stores/mints.ts for display labels
5. Ensure compatibility with Intl.NumberFormat for all supported currencies
6. Add appropriate currency symbols and formatting

Benefits

• Broader international support
• Better user experience for non-USD/EUR users
• Consistency with existing fiat currency implementation pattern

Notes

• Different currencies have different subdivision systems (most use 100, but JPY has none)
• ISO 4217 currency codes should be used for consistency
• Currency formatting should respect locale-specific conventions via Intl.NumberFormat

[prusnak]

Is this about minting fiat or showing fiat balances for bitcoin-backed mints?

If it is the latter then this had been already done in #415

[slekrem]

Thanks for the clarification question @prusnak!

This issue is about minting actual fiat currencies (like the current USD and EUR support), not just displaying fiat balances for bitcoin-backed mints.

Context

Currently, cashu.me supports creating invoices and minting tokens in USD and EUR units (where 1.00 USD = 100 amount, stored as cents). This is handled by:

2. activeUnitCurrencyMultiplyer in src/stores/mints.ts:233-241 - defines the multiplier (100 for USD/EUR)
3. formatCurrency in src/stores/ui.ts:106-107 - converts back for display (divides by 100)
   When a user creates an invoice with unit: "usd", the mint receives a request for 100 amount units (representing $1.00).

Proposal

This issue proposes extending this same pattern to additional fiat currencies that mints may support:

• GBP, CHF, CAD, AUD (all use 100 subdivisions)
• JPY (no subdivisions, multiplier = 1)
• Others as needed

This is different from PR #415 (which shows bitcoin balances in various fiat currencies). This is about actual fiat-denominated ecash tokens, similar to how stablecoin mints work.

Use Case

If a mint supports GBP as a unit (similar to how some mints support USD or EUR today), users should be able to:

1. Request invoices in GBP
2. See balances displayed as "£1.00" instead of "100 GBP"
3. Send/receive GBP-denominated tokens

Testing

You can test this with additional currency units on my mint: https://nutmarkets.sup3r.cool/

This mint supports various fiat currencies beyond USD/EUR, which currently don't display correctly in cashu.me due to the missing currency multiplier configuration.

Does this clarification help? Happy to discuss further!

[prusnak]

This issue is about minting actual fiat currencies

changed the title to read "add support for minting additional fiat currencies"

[prusnak]

• activeUnitCurrencyMultiplyer in src/stores/mints.ts:233-241 - defines the multiplier (100 for USD/EUR)
• formatCurrency in src/stores/ui.ts:106-107 - converts back for display (divides by 100)
  When a user creates an invoice with unit: "usd", the mint receives a request for 100 amount units (representing $1.00).

I think it should be trivial to expand these two functions to include all currencies from https://en.wikipedia.org/wiki/ISO_4217 - this also defines number of decimals (minor unit).

[prusnak]

proposed fix in #450