You can use
- SESSION_CONTEXT('LOCALE') -> ISO-Code
- SESSION_CONTEXT('LOCALE_SAP') -> SAP encoding
in your CDS view where clause.
If you need more flexibility it would also be possible to add a calculation view with a parameter on top of your CDS view. With the parameter you are able to restrict the output (e.g. by language). How you pass the parameter to the OData service can be found here: OData Parameter Entity Sets - SAP HANA Developer Guide for SAP HANA Studio - SAP Library