Uh-oh, I smell Russian English...

Yep!!! https://www.google.com/search?sxsrf=ALeKk01bUflrZ0smvybGR_tCO_a5zhzd5Q%3A1601474093100&ei=LY50X-3UBcuWsAXS75GYCw&q=%22One+trouble+with+EU+as+a+whole+is+that+what+served+a+club+of+six+or+nine+well+enough+no+longer+looks+adequate+for+a+club+of+15.+Let+alone+one+of+20+or+25%2C+especially+one+with+so+many+responsibilities.%22&oq=%22One+trouble+with+EU+as+a+whole+is+that+what+served+a+club+of+six+or+nine+well+enough+no+longer+looks+adequate+for+a+club+of+15.+Let+alone+one+of+20+or+25%2C+especially+one+with+so+many+responsibilities.%22&gs_lcp=CgZwc3ktYWIQA1D7kAhY-5AIYMuqCGgBcAB4AIABbYgBbZIBAzAuMZgBAaABAqABAaoBB2d3cy13aXrAAQE&sclient=psy-ab&ved=0ahUKEwitn77zg5HsAhVLC6wKHdJ3BLMQ4dUDCAw&uact=5

Yep!!!

Well, well ...
https://www.google.com/search?client=firefox-b-d&ei=pq10X7KPHoXnxgPLl5uIBw&q=%22what+served+a+club+of+six+or+nine+well+enough+no+longer+looks+adequate+for+a+club+of+15.%22&oq=%22what+served+a+club+of+six+or+nine+well+enough+no+longer+looks+adequate+for+a+club+of+15.%22&gs_lcp=CgZwc3ktYWIQA1DGJVjpNmC9OmgAcAB4AIABdogB1AGSAQMxLjGYAQCgAQGqAQdnd3Mtd2l6wAEB&sclient=psy-ab&ved=0ahUKEwiy-sb1oZHsAhWFs3EKHcvLBnEQ4dUDCAw&uact=5

3rd result from the top.
The thing is that the majority of such texts in these Russian textbooks in fact originate from foreign sources.

Agreed! The difference is that that the original sources are in correct English, with articles and punctuation intact, and the Russian versions are like this post. I’ve learned to spot them miles away.

Yes, and if you look at your link, all those sites are Russian!

Well, at least "the" is missing in the original too.
I have to admit, it was one long sentence in the original indeed.

Yes, deleted that comment.

Actually, the original has “the EU.” It wouldn’t be English without it. https://www.google.com/search?client=firefox-b-d&ei=pq10X7KPHoXnxgPLl5uIBw&q=%22what+served+a+club+of+six+or+nine+well+enough+no+longer+looks+adequate+for+a+club+of+15.%22&oq=%22what+served+a+club+of+six+or+nine+well+enough+no+longer+looks+adequate+for+a+club+of+15.%22&gs_lcp=CgZwc3ktYWIQA1DGJVjpNmC9OmgAcAB4AIABdogB1AGSAQMxLjGYAQCgAQGqAQdnd3Mtd2l6wAEB&sclient=psy-ab&ved=0ahUKEwiy-sb1oZHsAhWFs3EKHcvLBnEQ4dUDCAw&uact=5

Personally, I’m surprised at the amount of energy you’ve put into trying to prove me wrong. Do you not trust my English?

You are right. My apologies.

Starting a sentence with LET ALONE is like starting one with НЕ ГОВОРЯ УЖЕ, which I don’t think makes sense in either language.

Nothing to apologize for! These Runglish posts are disconcerting on every level... and you’re still one of my favorite people 😉

I trust YOUR English, but you often disagree even with native English writers. This time you were right, but Russians aren't the only ones that make errors.

In Russian you can easily start a sentence with НЕ ГОВОРЯ *УЖ* - if it was preceded by a pause.

В интернете много примеров, в т.ч. в reverso.
+https://english-grammar.biz/dictionary/ru-en/не+говоря+уж+о.html
+ ..

I do often disagree with English writers, or more specifically, with their editors and the things they allow to pass as correct English. If you assume that everything that’s in print is perfect English, you’re doing yourself a big disservice. Quite aside from the fact that something written in another decade is not longer acceptable. The other day, I was reading a modern book where the author stated something to the effect of “Today’s youth must needs decide to make spirituality a part of their lives since less and less parents are instilling a spiritual culture in the home.” Must needs??? In this day and age? Nope! I don’t know who’s worse - the writer or his editor.

Grumbler, there’s a big difference between NOT TO MENTION and LET ALONE in terms of where they can go in a sentence. In this post, they put LET ALONE at the beginning of a separate sentence and that’s a no-no. https://context.reverso.net/translation/english-russian/let+alone

So I guess I was referring to не говоря УЖЕ exclusively.

ngram со мной не соглашается, но для меня "не говоря УЖЕ" звучит неестественно и во всех примерах, которые я вижу, означает то же самое, что и "не говоря уж".

Следует отметить, что результаты для "уже" почему-то в основном из околонаучных книг.

👍🏼 interesting!