Request Network allows you to support any currency. Head out to the currency package to see how we identify and manage currencies in the CurrencyManager. You don't need to add new currencies in this repository.
Instead, when instanciating the CurrencyManager, you can feed it with a list of supported currencies for your dapp:
const list: CurrencyInput[] = [
{ type: RequestLogicTypes.CURRENCY.ETH, decimals: 18, network: 'anything', symbol: 'ANY' },
];
const currencyManager = new CurrencyManager(list);
To implement new types of currencies (aside fiat, BTC, ETH, ERC20), head towards payment networks.