Is There A Point For English-Speakers To Learn Other Languages
The explanation for this is obvious. English is the most widely known language in the world, and most foreigners they come in to contact with know English, with varying degrees of proficiency. Why bother trying to learn the languages of foreigners, when they know yours, is probably what most British think.
Given the amount of effort that learning a new language requires, they are probably in most cases right. However, there are still upsides to knowing other people's languages even if they know yours. This clip form the movie Braveheart (which BTW is my favorite movie of all time) illustrates this.
Here Scottish national liberation leader William Wallace meets with Princess Isabella, the daughter-in-law, of Wallace's enemy King Edward I (usually referred to in the movie, including this clip, as "Longshanks"). After she accuses him of atrocities, he defends himself, by saying that the city he seized was used as a staging point for invasions of his country and that the royal cousin they executed had killed innocent Scots and that "Longshanks did far worse the last time he took a Scottish city".
Isabella's companion, Lord Hamilton, tries to defend his king, by saying in Latin that Wallace is a murdering savage that is lying. The reason he said it in Latin, instead of English was of course that he didn't want Wallace to know he said it and he assumed that Wallace didn't understand Latin. To both Isabella's and Hamilton's great surprise, Wallace understood what was said and replied to them in Latin. As Isabella and Hamilton was silent, in chock, Wallace then said ou en français si vous préférez, which is French for, that they could speak French, if that's what they preferred, revealing that he could speak French as well as Latin. In the English upper class at that time, most knew French and Latin (and Isabella was BTW the French King's daughter, so naturally she knew French), but among common English and Scot people, most knew only English which is why they didn't expect that Wallace had learned Latin or French.
The point is that even if others know your language, knowing theirs is, all other things being equal, also positive since it enables you know what they're talking about if they switch to another language, or what they're writing about in other languages, whether intentional to exclude you (as in this clip) or not.