"Only report to me in ASD-STE100 Simplified Technical English."
I'm not sure how true this is, but when using "forced" json output it def had a big drop off in quality - https://arxiv.org/html/2408.02442v3.
I think you're better not fighting it with hacks like this and find a different model.
Based on that paper, I would maybe try to check if it was true for a modern use case, I would very much not assume it was still true.