The Greek that is translated in English as “(my) true son in the faith” is translated into Arop-Sissano as “son lamat in the faith.”
Nystrom explains: “In Arop, if you want to talk about the real essence of something -– its most important part -– you talk about the lamat of it. Arops say, ‘I don’t want to tell you everything they said at the meeting, but the talk lamat is like this,’ and they proceeded to tell you the main point of what was said. (…) Here Paul is saying that Timothy is his true son, his son in every important way.” (p. 198f.)
See also flesh (John 1:14).