A lot of schools offer you the opportunity to learn a foreign language while studying. As a part of your GCSE and A-levels you can also study a foreign language. You may think that this is just to improve your documents and student profile but once a language is learnt properly, you cannot forget it even if you don't use it frequently. It has been found in research that students who study your language are very less likely to forget that language even after 40 to 50 years of learning that language and not even using it on a regular basis.
You are probably more likely to remember a foreign language than your basic math concepts including algebra and geometry. By learning a rampantly used language like French or Spanish, you can become a global citizen. There are many languages other than English that are used in different parts of the world. If you are somebody who loves traveling and interacting with people then learning a language will be very beneficial for you. You can also pursue the profession of diplomacy and foreign representatives from your country side.
