Do speaker wires have to be the same length for each speaker?

It won't make a difference in any normal setup. But my OCD could never handle the asymmetry... 

Same length speaker cable 

not necessary!

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great sounding 

 custom at a v low cost 

Not unless your ears can detect a phase difference of about 3 nanoseconds per meter difference. 

This is almost as entertaining as a closely matched UFC bout.

I prefer same length, but I need to ask the OP: "Why NOT the same length?"

If you're running in-wall, got it.  But if not in-wall, you've got plenty of space in your listening room if you have to drape/coil/hang/etc. (there goes another discussion...) the excess on the longer side.

Having one shorter than the other would be better than splicing to make them the same length.