Don’t get alarmed! It is just a funny article on a newspaper.
An immersion programme on a football pitch … will this work?
I suppose that depends if they are actually committed and genuinely motivated to improve their English or not. However it is true that ‘language cliques’ can divide cohorts and cause serious problems. It’s something I have encountered in my work in various international summer camps. At a camp in New York we had a few kids from Mexico who put no effort into their English and would keep switching back to Spanish at every opportunity. It really divided the group and turned everyone against them. They felt left out. The directors response was to simply ban all languages but English. Unsurpisingly, it failed.
Middlebury College runs summer programs for foreign-language learners with a nothing-but [insert relevant language here] rule that works. You give your word of honor when you arrive that you will use only the language you signed up for, everywhere, and that’s it. (When I needed to go to the infirmary, one of the staff had to go along as an interpreter.) Before I arrived I knew the grammar and had a decent passive vocabulary, but would not speak outside of class. By the time the course ended (about a month later), I still had to paraphrase a lot, but it was Russian.