At work, I speak English every single day (and also a wee bit of German). The time I speak English is in the realms of 50-90% of the day. When speaking to colleagues, partners and customers, coming from many countries including The Netherlands, England, Bangladesh, India, Pakistan, Austria, Germany, USA, Switzerland, Sweden, Denmark and Ireland I feel that I master the language: I can do presentations for large audiences, discuss any work related topic, defending my opinions and explore other people's point of view. In the canteen, I can always take part in the numerous, typical expatriate discussion topics like: language, cultural differences, alcohol prices, immigration policies, spare time activities and so on.
In my local environment, at work and at expatriate meetings, I feel I've got great control of the English language. Of course, I also feel I can improve significantly and I do indeed learn a lot from chatting with our native English speakers, but still, I feel totally confident using English as the main language.
Whenver I go to my third home country Scotland to catch up and hang out with Scottish friends, I instantly get reminded of exactly how much English I don't know, how much my English has deteriorated since I lived here (first of and foremost the flow and speed), how fast the conversation twists and turns and how fast I need to construct my argument when joining a vivid four person discussion.
Speaking English in an environment of mostly non-native speakers is ridiculously easy. First of all, it's nice and slow, the conversation topic stays on track for a long time and it's easy to follow the natural progress of the conversation. Secondly, it's forgiving; people are used sentences and words being a bit off and often several people present will know the word or sentence you meant to say (since they know your language and/or culture) and will do the "search and replace" for you. And finally, the references given like quotes, politicians, TV series, advertisements, food and drinks are known to most of the people present, regardless of their nationality (at the very least when everyone comes from the same continent).
It's great being back in Scotland, it's a lovely place to be, wonderful people, terrible weather, great accents, colourful language and a great reminder of exactly what it takes to master the English language