Lumenswap is an open-source and decentralized client which supports all of the assets on the Stellar Network.
You can add an asset pair to the spot in two ways:
On the asset pair modal page, click on add custom pair button. Then, enter the values of asset issuer and asset code for base asset and counter asset. Next, click the add pair button.
Using the following format, you can enter an asset pair page in the spot section.
When one of the assets is XLM: