It really is going to depend on how verbal your child is to begin with. Many autistic children on the more severe end of the spectrum, can't even verbalize/communicate in a primary language, so attempting to get them to learn a second one, isn't even an option.
If your child has good verbal skills, then they would probably pick up a second language just like any other child would, but if they are already struggling with communication skills in one language, I'd be hesitant to introduce another.
Best thing to do would be to talk to your child's speech therapist (if you have one). Otherwise if you want to try introducing another language, there are plenty of kid friendly videos that you could try.