For 
in 
I was unfamiliar with this word. Though I might have heard it before, it happened during live speech and I was guessing its meaning from the context. Today, however, I learned it sot of "in your face".
Cleft is a synonym of a split. Like, for example, cleft chin.
So cleft goes with a physical attribute, but I don't know if it goes with mental attributes. So correct me if I am wrong, yet in the meanwhile, I will assume so.
Having this in mind, the type of cleft I will talk about is the split that happens in the mind of a bilingual person when they (he/she/...) are attempting to express their thoughts in a language media.
Let me explain... Many times people ask me in which language I think and get surprised when I answer that I don't think in a language, and for that matter, I don't think anybody does.
That becomes obvious when you try explaining someone a solution to a math problem or something of the sort. Most likely you will point your finger to the tricky substitution and say "here you add this to this and then on this line you do this" rather than to explain it in real mathematical terminology. In other words, in the case of math, you don't need to convert your idea into the word strings applying the grammar rules, because you can understand the idea faster and easier just looking at the formulas.
Similarly one can interpret the silent clues that the other person could show us during a conversation. Let's say is a person rolls her eyes you know that she means that she disagrees with the speaker, but cannot do anything under the circumstances.
When we talk we translate the images and logical structures that operate within our minds into a linguistic code that the other person can interpret thus transferring this code into imagery and logical structures inside their mind.
Now then, when a bilingual person attempts to convey their thoughts, both languages line up their linguistic constructions providing what I would say "a cleft of possible expressions."
That's why it often happens when two bilingual people speak with each other using mixture languages such as the so-called "Ruskish" or "Spanglish."
They do it since one part of the phrase is easier to deliver using the words and the construction of one language and the other part using the words and the construction of another one.
So it goes...