Dual language js problems

Hello all

I have a Freelancer guy enabling a dual language option on my site which uses the Highend theme. He initially stated the work would take 2 days but 10 days later is still having problems. He’s claiming it works on his dummy server but there are issues with some js and the theme which are preventing it from working for me.
I’m not knowledgeable on this subject to know if his issues are genuine or whether he’s approaching the project from the wrong direction, as my initial research led me to believe the work required was to do with database instructions.
I would be grateful if anyone can comment.