教父 is a 100% foreign word, translating from godfather. 教 means religion or religious, and 父 for father. 教父 means the a man who serves as sponsor for a child at baptism (copied from Dictionary.com Unabridged, 2016), or the leader of a criminal group, especially a mafia family (copied from
Cambridge English–Chinese (Simplified) Dictionary). 干爹 is not that scary, just
adoptive father (traditional adoption, i.e. without legal ramifications) (copied from MDBG). In your case the choice of word is absolute 干爹 but 0% 教父. You mentioned that some dictionaries translate both 干爹 as godfather, which is at the first sight surprising but reasonable after a thought, since that 干爹 could also mean a mafia guy much older than of the 干儿子, who is another mafia guy. Hence it is logical to translate it into godfather. However, when 干爹 is translated as godfather its meaning is related with the mafia, and 教父 has no interpretations for adoptive father. Clarification of the two words is shown below, among which only b.2. is appropriate for the context.
a. 教父
- A man who serves as sponsor for a child at baptism (copied from Dictionary.com Unabridged, 2016).
- The leader of a criminal group, especially a mafia family (copied from
Cambridge English–Chinese (Simplified) Dictionary).
b. 干爹
- Adoptive father (traditional adoption, i.e. without legal ramifications) (copied from MDBG).
- A mafia guy much older than of his 干儿子, who is another mafia guy, but it is not about the adoptive and the relationship between them would usually not very close as between real adoptive family. They even don't live together. More about office politics, where you try to entertain your boss.
我被他当做(了)自己的儿子。
just meansI'm regarded/treated as his own son
, while he doesn't have to be 干爹, godfather, adoptive father, and so on.I'm regarded/treated as his own son
is not the same thing asI'm regarded/treated *by him* as his own son
?I'm regarded/treated by him as his own son
.