If someone doesn’t know any other language then youay talk to them in Ivrit otherwise it’s assur
I have some very frum Sephardic neighbors. They have a picture on the wall of their son meeting Rav Ovadiah Yosef at his Bar Mitzvah. While the parents are from Israel all the children are American. They speak english and Hebrew. I asked the son over Shabbos when he met Rav Yosef what did he speak to him in. The Son told me Rav Yosef spoke to him in Hebrew (I dont know if Rav Yosef knew english or not).
The father of this family prefers when I go over there on Shabbos that I speak only hebrew and prefers only hebrew spoken by his children as well on Shabbat. Of course this is not entirely possible and some english is spoken