I would to know what are luggage allowance for international flight by Swiss Airlines Economy, class L from San Francisco, USA to Zurich, Switzerland and then to Riga, Latvia. Thank you.
Given that the flight you're asking about departs from the US, then it is a legal requirement that your ticket receipt contains the details of the baggage allowance. The allowance will be the same for both the flight from the US to Europe, and then the intra-Europe flight, presuming they were both purchased on the same ticket.
Presuming you have already purchased the ticket, then check your receipt and it should have the details of the included baggage allowance.
If you have not yet purchased your tickets, then you can check on Swiss's website for the expected allowance for your trip. Once again, the allowance for the International leg will also apply to the intra-Europe leg.