I’m thinking of becoming a speech pathologist, do I need to learn sign language?

You don’t need to know sign language unless you are really interested in working with the hard of hearing. It might come in handy if you have a client whose parent(s) is/are deaf, but other than that it’s definitely not a necessity. You can always communicate thru writing and many deaf adults can lip read very well.
The spanish isn’t a bad idea, but to be honest, SLPs are in such high demand, no extras are even needed.