url query only has one “?”.
specialites?locale=${language}?filters
specialites?locale=${language}&filters
try this:
const results = await fetcher(
`${process.env.NEXT_PUBLIC_API_BASE_URL}/api/specialites?locale=${language}&filters[Slug][$eq]=${slug}&populate[0]=resultats&populate[1]=Illustration&populate[2]=resultats.Image`
);