https://developers.ripple.com/cross-currency-payments.html
Cross-Currency Payments
跨币种支付
In the XRP Ledger, you can send cross-currency payments that exchange one or more issued currencies, XRP, or both. Like direct XRP payments, these payments use the Payment transaction type. Cross-currency payments within the XRP Ledger are fully atomic, meaning that either the payment fully executes or no part of it executes.
在XRP总账网络中，支付发送与XRP或一种多种已发行货币的付款，与直接进行XRP付款一样，跨货币付款使用Payment交易类型。XRP总账网络中的跨货币付款完全是原子的，也就意味着支付只能完全执行成功而不可能部分执行成功。
By default, cross-currency payments deliver a fixed amount to their destination at a variable cost to their source. Cross-currency payments can also be partial payments, which deliver a variable amount to the destination within a fixed sending limit.
默认情况下，跨货币付款基于可变的交易成本并发送给目的用户的确定的固定额度。当然，跨货币付款也可以是部分付款，在固定付款限额内发送可变的付款金额。
Prerequisites
先决条件
By definition, a cross-currency payment involves at least two currencies, which means that at least one currency involved must be a non-XRP issued currency.按照定义，跨货币交易至少包括两种货币，且至少包括一种非XRP的已发行货币。
Typically, this means using one or more currencies issued by an XRP Ledger Gateway. Such currencies are backed by funds outside the XRP Ledger, and can be withdrawn through the gateway.通常，用户持有的一种或多种XRP总账网络中发行的货币，该货币可以在XRP总账网络以外的网关服务商处进行提现操作。
You could also use digital tokens that are only issued within the XRP Ledger and has no outside backing, as long as the parties transacting are willing to send or receive those tokens and treat them as something of value.一种情况是，只要交易双方都愿意在XRP总账网络中发送和接收这些数字资产，并认可其价值（资产数字化），用户也可以不必转出至外部。
There must be at least one Path between the sender and receiver, and the total liquidity across all paths must be enough to facilitate the payment. For cross-currency payments, this usually means consuming Offers to convert from one currency to another.在付款发送者和接收者之间必须有至少一条交易路径，且交易路径所带来的流动性应当足以促成交易。在跨货币付款中，这通常意味着消耗Offers（报价单）以实现一种货币转换为另一种货币。
Autobridging
自动桥接
Cross-currency payments that exchange two issued currencies automatically use XRP, when it decreases the cost of the payment, by connecting order books to deepen the pool of available liquidity. For example, a payment sending from USD to MXN automatically converts USD to XRP and then XRP to MXN if doing so is cheaper than converting USD to MXN directly.
跨货币支付自动使用XRP来作为两种已发行货币的中间媒介，以降低付款成本，同时使用order book增加已发行货币的流动性。举例来讲，如果使用XRP作为中间媒介转换的成本，比直接进行USD及MXN兑换更低的话，付款自USD兑换成MXN的过程就会首先将USD兑换为XRP，然后再将XRP兑换为MXN。