Invisible on Facebook (hide from chat)?

[White Raven]

I never go on FB for real time chat, only to catch up on news and posts. Last night I went on it just to look up the phone no. to pay for some private lessons for my son. All of a sudden an in-law that I have not yet met (newly married into the family) who I friended starts chatting with me. And because we don't speak the same language, I had to open a translator device and go through all this trouble for the usual "hi how are you" routine. Please help - how can I make myself invisible when I'm online so people stop chatting with me when I go on?

I want my chat box to be like an e-mail box - I can reply anytime I want, but not real time.