Kareyku employs what is called a Topic Marker. This marker varies greatly depending on the language, in the case of Kareyku it not only serves to mark the topic of a statement, but also can be translated as "in regards to" or "talking about...", so for instance you can use it in a sentence like
mas-ejen qappa-ka-l pilé
food-TOP eat-2TR-EVD fish
Regarding food, I'm known to eat fish
It can also mean "I prefer fish" or "I like fish the most". The topic marker being -ejen and replacing any final vowels, it can also be used with pronouns, in which case they have some different kind of forms, so ikan '1st sg.' would turn into ikejen and pen '2nd sg.' would be pejen. So, as can be seen it is used to specify.
kar-ejen tana-ka-ch Karey-qa
speech-TOP speak-2TR-EVD Kareyku-INSTR
As regards to languages, I speak Kareyku
This last one uses the suffix -qa which means 'by means of' and is used in such constructions. Note that the name Kareyku will be rendered Karey- when any suffixes are used. It can also be used in other senses, for example with the question adverb to specify the subject of the question
What are you talking about?
And this would be answered of course using the topic marker, so
about a house/houses
Always remembering that it can refer to a single house previously mentioned or maybe to houses in general, depending on the context.