To enable the Euro symbol (€) in Strategy Developer, perform the steps below:

After this setting is applied, when Strategy Developer is launched, the Euro symbol will be available as a currency symbol in the formatting properties of the metric editor, as shown in the screen shot below:

Note: The dollar ($) and Euro symbols cannot be used at the same time on the same report. But since Strategy 9.0, multi currency symbols are supported in one report by directly typing the code of the symbol in metric formatting editor. Refer to Technical note below for more details:
KB31778: How to display the Euro sign without changing the Regional Settings in Strategy