Also I was wondering about "kepeken", is that used instead of the particle "e" before a language because you're saying that you talk using that language as opposed to talking at it? It makes sense to me but I wanted to make sure that that was the grammatical reason before I start using it like that.
There are only about 7 places to put a word that goes with a verb, DO and the 6 prepositional phrases (maybe subject, see below). In a natural language, there is enough corpus that people can get used to instrumental or direct object syntax being used interchangably- in a conlang, especially one that isn't supposed to be a relex of English, we have to rely on the specification and be wary of the community corpus, especially if people are just doing what they do in their mother tongue.
I speak French. (Direct object-- we've just gotten used to this in English.)
I speak in French. (locative, but a language is only metaphorically a place)
I speak with French words. (awkward, but clearly instrumental)
So typically this is explained as words having a semantic role (subject is doing the action, a sort of agent, instrumental answers to what tool was used-- direct object answers to what was on the receiving end of an action-- a sort of patient) and a syntactic role and they don't necessarily match up.
When a prepositional phrase exists to make clear the semantic role, it's good style to use it and make every effort to keep the semantic roles matched up with the syntactic ones.
And it occurs to me that sometimes the word that goes with the verb can/could go in the subject.
I don't think the grammar of tp is nailed down enough to decide which of the following is better.
1) mi pakala e ilo. I broke the machine.
2) ? ilo li pakala. The machine broke-- something broke it, but what is was isn't so important. This means pakala works like English and has a middle voice!
3) ? mi tawa wawa e ilo. ilo li pakala. The machine was clearly broken my actions, but it is the subject slot, where normally we see agents!
4) ? ijo li pakala e ilo. Something broke the machine.
5) ? ilo li pakala sama. The machine broke itself. Seems to overemphasize the agency of the machine.