There are two ways to set the default currency for your store:
1. Set the default currency under Admin Panel > Start menu > Definitions > Currencies for the store.
Figure 1. Set the default currency under currencies module
Currency Value serves as exchange rate. Thus the store must have a default currency, US Dollar for example. In this case the currency value of US Dollar is 1.00. Values of other currencies can be entered manually or updated according the real change rate automatically.
2. Set the default currency under Admin Panel > Start Menu > Definitions > Languages for each language.
Figure 2. Set the default currency under Languages module
If there is just one language supported in your store, you just need to set the default currency in the currencies module because the customer can’t change the language in the store front. But, if there are several languages in your store, the default currency set in the languages module will override the setting in the currencies module.
For example, if your store support two languages(English and German), the default currency for English is US Dollar and Euro. And the default currencies set in the currencies module is US Dollar. When the customer click the German language flag to change the language, the default currency of store front will be changed to Euro. The default currency set in the currencies module is ignored.
You may want to use just one default currency for their. You don’t want to use the default currency for each language. In this way, you have to set the ‘Use Default Language Currency‘ to False under Admin panel > Start Menu > Modules > Services > Currencies as follow:
If you want to use the default language for each selected language, you have to set the ‘Use Default Language Currency‘ to True. And then, you should set the default currency for the each language under Admin panel > Start Menu > Definitions > Languages.
Now, whenever you change the language settings, it is unnecessary to clear the cookie or cache of the store front. It will affect the store front immediately.