I too lived in several foreign countries. During that time period it was continuous, daily, hourly. I lived in a host nation apartment, foreign landlord, shopped at foreign grocer, used public transportation, etc. Honestly, don’t overthink it. Contact on a professional level is one thing, when the relationship moves more towards personal it moves closer to reportable. I follow the simple rule of “if it is explainable, it is understandable.” If you work in a foreign building filled with foreign people (technically you are the foreign person, but I digress) and the contact is incidental such as moving along the corridor, going to use a restroom, eating lunch…it isn’t an issue. When a coworker moves beyond work acquaintance and towards friendship…one you break bread with at home, recreate with, go to movies, tour…that is when you need make certain to report it. For the facebook thing, perhaps print the friend list after judiciously removing those who are more hangers on from certain pages you follow…but do not interact with…highlight the ones you communicate with, send messages to and from. Let the investigator scope the ones they feel require scoping.
Likewise when listing character references I inform applicants if you know the person enough to use as a character reference then list the date from when you met them to “present.” Don’t put a given end date. I had packages rejected claiming the person no longer had contact after a certain date. There really isn’t a hard and fast rule as to how many times one must be in contact or how recent that makes it continuous. I may go weeks without talking to my lifelong best friend. Suddenly, I may have 3 emails a day. I consider us “in contact.”