What is the ruling on this relationship with a foreign girl via chat, and what is the way to convince a friend who is committed to worship to abandon it until he marries her after she completes her studies?

It is not fitting for a person who is observant of prayer and fasting to engage in inappropriate relationships. This brother should be advised to cut off these relationships, which are snares of Satan, and that committing forbidden acts by someone like him is more egregious. His prayers and fasting should deter him from indecency and evil. If he wishes to marry the girl, he should propose to her lawfully and cease contact with her except for necessities related to the marriage, and it is better for this to be done through her guardian.