Brazilians write laughs in several ways (almost infinite), the spellings are "personal" onomatopoeias, being the most common I see: "hehehe", "hahaha" and "kkkkk".
The "h" has the sound as in the word hat in English, so similar to the sound of: risos, rato, retorno, etc in Portuguese. I believe this is a foreignness, from English. But look below the problem of using the "r" in Portuguese in the middle of the word.
ONOMATOPEIAS (FREE NEOLOGISM)
There are several variations of "hehehe" or "hahaha" using all vowels and some combinations like "hihihi", "huhuhu", "hauhauhau", "hoehoehoe", etc. There are also variations of the replications with and without the spaces like: "he he he", "hehe", "heheheheheheh...".
There are also the "kkkk" which is pronounced as "ca ca ca ca" using just the ca from word car, which is a natural pronunciation of k in Portuguese.
Rarely but used, are the onomatopoeias using the "r" instead of "h", like: "rarara", "ririri" ("rerere" I haven't seen yet, but is possible). These form has a problem to be correctly pronounced in Portuguese because just the first "r" has the sound of h like in hat, the others have the sound if r in rat. So, its strict pronunciation is English would be something like "ha ra ra", from ha(t), ra(t). To be more correct it should be written with spaces "ra ra ra", now this "ra" has the sound of ha(t) in English, and so could be an pseudo-onomatopoeia.
As free onomatopoeias, I have some friends which prefer to be unique and write things like "quiquiqui", "cacaca", "kaukaukau". So, there are many others.
The spelling variations may have a lot of motives, being the main: personal preferences, as people laugh differently can be a try to imitate it. But there are others like cultural of a group, or imitation of friends from a group, like the explanation for memes to be spread around the world. I have the example of the word "casul" which became common in Brazil just in the world of games to refer a newbie player, the origins is from "casual player".
As a meme, few people (or nobody) knows its origins either meaning (or pronunciation), so the pronunciation of "huehuehue", can be (the most probable) an English pronunciation or any adaptation to sound like an onomatopoeia for laugh.
There are also the word "risos" (laughs), usually in plural, written as an informal (incorrect) abbreviation, like: "rs", "rs rs", "rsrsrs", and several others replications and combinations.
The full word risos is also used, with some exceptions, usually among parenthesis or braces like: (risos), [risos]. These forms is usually written in the final of the phrase like: A festa ontem foi maravilhosa, adorei relembrar as histórias do colégio (risos).