Have you heard Jackie Chan speaking in English in the Hollywood movies??
Since he is chinese, his accent is not exactly the same like the native speakers.
The question is, How did he do it?
In case if you forget, all male and female actors who act in a movie are required to memorize their lines from the provided script. Basically, if the actors do not speak English, they just keep on practicing their lines until they can somehow memorize the pronunciation and the intonation of the words properly. Once the movie is published, you would see the lines are well rehearsed and to certain extent, the actors' dialogues seem very authentic and almost native like. Speaking of practices make perfect.
So what are you waiting for?
Start memorizing the lines taken from your favourite English movies.
Stand in front of a mirror and read out the lines by heart.
Next time when someone invite you to join a conversation in English language, you would know how to response effectively.