The legality of businesses accepting Bitcoins from international customers may depends from one country to another. The first approach would be to research online on the legality of accepting and transacting in Bitcoins and possibly utilizing a payment processing service like Bitpay for example to receive Bitcoins from customers and have it instantly converted and transfered into the companies bank account (Current account). There's a good case study here - https://blog.bitpay.com/b2b-bitcoin-payments/ on how a US cosmetics company could've used Bitcoins for receiving payments from Chinese customers which was a complex process of converting Yuan to Dollars in China and then send wire transfers from China to the US bank account. Also in general most businesses who accept credit card payments from international customers may require PCI checks for meeting security standards, these can also be overcome by using Bitcoins.

You could record Bitcoins as receipts under Accounts receivables or as a regular sales transactions with Bitcoin receipts instead of cash. There's a nice guide here on how to record receipts and payments (and deriving cost of goods sold) using quickbooks for Bitcoin transactions performed via payment processors like Bitpay - https://bitcoinmagazine.com/articles/using-bitcoin-with-quickbooks-part-1-recording-sales-and-accepting-payments-1385976677/