This is a formal translation for your sentence : "I have a friend in english country"
Here's an explanation why DL translation more precise
"Saya punya seorang teman di inggris" is grammatically correct for the translation, because "di inggris" we already knew there is a strong statement "di". So, this "di inggris" could only mean as a country "English" official known as "England"
While your translation "di negara inggris" is more appropriate as "in english country" & it may possible the "english country" is a country based on english language, also there are several country based english language, right? :)
I hope so this helps & If there's an implausible explanation, let me know
perhaps I could help