There is some research in bilingualism and code switching dealing with such phenomena. The main thing is that code switching is not just random or arbitrary but does follow some rules. For example, I once overheard a conversation between two young people in the tramway [some Turkish I don't understand] zum Beispiel [more Turkish I don't understand] (the ...
Transitivity is a hard concept to handle. Verbs like eat or drink seem like prototypic transitive verbs, but they occur in a lot of structures
He ate too much.
He ate for a long time.
He ate more than I did.
He's stopped drinking.
And verbs like run or walk seem like prototypic intransitive verbs, but they can also occur in a lot of structures
"Patient" is an adaptation of the Latin word for "undergoer", just like "agent" is an adaptation of the Latin word for "doer". This meaning of the word is found in all the dictionaries I've checked (1, 2, 3) and is inherited from the classical grammatical tradition.
The modern meaning, "someone who is undergoing ...