What percent I need to speak English professionally?

English is spoken by communities on every continent and on oceanic islands in all the major oceans. English is the dominant international language in science, business, aviation, entertainment, and diplomacy, and also on the Internet. In most fields of work your ability to speak English can help you advance your career; helping you get the job you want and earn more money. No matter what your area of expertise, skill in English will contribute substantially to your success. Speaking and understanding English will allow a person to communicate with each other, besides this it offers you more chances of doing professional jobs not in your own country but around the world.

You need a good vocabulary for sure. Growing up I learned that the more you read, the more you expand your vocabulary. I use to have a thesaurus and a dictionary handy so that when I read a word or passage that I didn't understand I could look them up and then re-read the passage so I could register it. If you take this advice, it may help you expand your vocabulary and I appreciate it when playing word games like scrabble or boggle. :)

If you're asking how important English is in today's world, English is the current most powerful or popular language for business and technology and politics. It hasn't always been this way. In fact, the term "lingua franca" refers to a time when French was considered the language of diplomacy and commerce, for instance. If you're asking what percentage ranking in fluency you should have, it depends largely on the context. If you're in a profession where basic communication is sufficient because both you and your audience have a common grasp of concepts, they'd likely be very forgiving in speaking and listening. If, on the other hand, your job is talking to customers or clients or patients with critical information, your comfort is not nearly as important as that of your audience, so you'd be well advised to increase your fluency or choose some other position. If you're talking to your friends, it's not likely important at all. So, sorry to say, my answer is, "It depends." But you have quite a bit of flexibility in the situation, right?

I agree with Mark. No matter where you are planning to work in the world, speaking and writing English professionally will provide you an edge to be able to work with international teams. If your aspirations are to work locally in a country, speaking that language only will suffice.

Depending on the field you are planning to pursue, English is definitely needed to be spoken 100% professionally. Every field have their own catch phrases like in IT, business, etc. and they are spoken in English.