The support of tone and writing_style for French, Italian, Portuguese and Spanish is already present in your DeepL Write Web Interface
https://www.deepl.com/en/write

but it is still missing for the Rephrase feature in the DeepL API Pro (only English UK, English US and German are actually supported).
It would be very helfpul if you could implement it soon.
Best regards.
Regis Barbier