Digital currency, also known as cryptocurrency, is a type of digital asset that uses cryptography to secure and validate transactions and to control the creation of new units. The development of digital currency has led to the emergence of a variety of programming languages used to write the code for these systems.

Bitcoin, the first and most well-known digital currency, was created using a programming language called "Bitcoin Script". Bitcoin Script is a stack-based, low-level programming language that allows for complex mathematical operations to be performed on the blockchain, which is a decentralized public ledger that records all bitcoin transactions.

Ethereum, another popular digital currency, uses its own programming language called "Solidity". Solidity is similar to JavaScript and can be used to create smart contracts, which are self-executing contracts with the terms of the agreement between buyer and seller being directly written into lines of code.

Ripple, a digital currency built on the Ripple protocol, uses a different programming language called "XRP-based" or "C++-based", depending on the source. The XRP protocol is built on the C++ programming language and uses a consensus algorithm called "Proof of Stake" to validate transactions.

Litecoin is another digital currency that uses a programming language called "Rust". Rust is a systems programming language that emphasizes safety, concurrency, and performance. Litecoin's use of Rust allows for faster transaction processing and improved security compared to other digital currencies.

Other digital currencies, such as Monero and Zcash, have been developed using different programming languages such as C++, Python, and Go respectively.

In conclusion, while there are many different programming languages used to create digital currencies, some of the most popular ones include Bitcoin Script, Solidity, Rust, and C++. These languages allow for complex mathematical operations to be performed on the blockchain and enable the creation of smart contracts and other advanced features. As digital currencies continue to evolve and expand, it will be interesting to see how they incorporate new technologies and programming languages into their infrastructure.