You can use Felix to translate HTML pages, of course, but whether it is the best tool for the job depends a lot on what you mean by translating a website.
If your client is simply looking to have you translate a few pages, you could ask that the pages be sent in a zip file or something, and then you could simply translate them in Felix.
Most websites are generated with content that is dynamically feed into page templates from a database, though, and depending on how the client wants to provide the source material, Felix might not be the best tool for the job.
If you can share a little more detail about what you have in mind, I might be able to offer better suggestions.
Best regards,
Sako Eaton