Yeah… I’m gonna use GOOGLE TRANSLATE as TTS since I’m too embarrassed to talk myself.
Not a lawyer here but my understanding is that it would be against the Google Terms of Service, but still legal as there’s no law that says you have to follow ToS.
Also realistically the scammer would have to report you and I doubt they’d want to send those call recordings over to the police 
You don’t have to talk to a scammer.
You can always call them and mute or put them on hold. It wastes their time, 30sec to a minute and makes them angry. If you have 3-4 fake numbers on rotation that’s enough to enrage them.
“Is it legal to make fun of scammers and waste their time?”
Yes, yes it is. They’re not operating a legitimate business. Really what you’re doing is a public service, by tying up their phone lines, they can’t use that line you’re talking to them on to scam people.
But don’t do that from the UK. The laws about libel and slander in the UK are insane. There was a scam baiter from several years ago that went by the name “ThunderTech” and he got into a whole lot of legal trouble. Since he showed his face publicly and the scammer in question had a lawyer in the UK, he got fucked by a slander lawsuit.
I’ll remind everyone reading this that Kitboga, Scammer Payback and Trilogy Media get doxxed constantly…Lots of bad people know who they really are, because they show their faces.
You’re not going to get sued following the scammer script and wasting their time. Even in the UK.
If you post their pictures or business names and say mean shit maybe.
Again, don’t listen to this guy.
Always use a VPN and never show your face if you’re going to be a scam baiter.