English is a highly important tool, which is strongly nesessary for everyone: managers, team leads, developers, HRs, etc.
Most of the good learning materials are in English. So, great English is an absolute pre-requisite. Now, how do you get there? First, understand where you are now. You can reach out to the language schools and test yourself. Their tests are free. Covering around 10 assessments will give you an idea of your current level. Depending on this, set targets for yourself, create a plan and act on it. For example, scoring high on IELTS or TOEFL (e.g. over 8.0 and 110 respectively) would be a quite challenging yet rewarding goal. That score will let you feel very confident about your English and you will have no problem communicating with any English-speaking person. Alternatively, you can decide to reach advanced / proficient level. For example, if your current level is upper intermediate, setting the goal of progressing to the advanced in 6 months is cool. Whatever target you set, do not forget to master all 4 areas: speaking, listening, writing and reading. Also, speaking clubs (starting from upper intermediate – with the native speakers) is a great instrument to stay on top of your speaking. Some of them are free by the way. On the Internet, there are a variety of materials (many of them are free) for people who want to improve their English.