Since WPL3.1.0 we added a Currency Switcher Widget/Activity for switching between currencies. In order to enable this feature, you can simply add its widget to one of your website theme sidebars.
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After setting up the Unit Switcher Widget or activity, your website's users are able to change the currency and see the prices in their desired currency. Also, the search widget will change the price field accordingly.
Note: Right now, this feature works only for Currency units. So don't try it for other unit types.