On the Report you can set the Language Property which is in the Localization section. You will place the language code like en-GB in this property. You can also do this at the field level too if you want. This should pick-up on your Regional and Language settings on your PC. If you want to override this or control this then you can simply set the report property accordingly.

If you set this property and then view the code of the report (RDL) you will see this towards the very bottom:

en-GB

This information will be used for currency, date, and numeric conversions.