Amusingly, I think this phrase illustrates your point. To the best of my knowledge, a native speaker (which I'm not) would always say "The whole book is (in?) English", leaving off articles seems to be very common for Slavic people (since I believe you don't really have them in your languages).
leaving off articles seems to be very common for Slavic people
Whenever I come across text that has a lot of missing articles, the voice inside my head automatically changes to a Russian accent; and in the instances where I've bothered to find out the author, it was always someone from Russia or some other ex-USSR country, so it seems I've already ingrained this characteristic at a subconscious level.
I think this is more about formality and modern usage. I'm nearly 50 and am British. I sometimes write in this abbreviated form, omitting things like articles when they are unnecessary. Especially in text messages, social media posts, etc.
I used to work in academia with a Chilean guy who added extra articles where they weren’t needed and a Slovakian guy who didn’t put any in at all. I had fun editing the papers we wrote!
Spanish has definite and indefinite articles like English, so at least the concept is not unknown. However, even then, the correct usage is sometimes really arbitrary and varies across languages, e.g. why is it typically "mankind" and not "the mankind" (by contrast, in German it's "die Menschheit", with an article)?
Amusingly, I think this phrase illustrates your point. To the best of my knowledge, a native speaker (which I'm not) would always say "The whole book is (in?) English", leaving off articles seems to be very common for Slavic people (since I believe you don't really have them in your languages).