Pronunciation of "Makemake" versus "make"

"Makemake" is the name of a celestial object, a dwarf planet.

The "i" in name "Makemake" is pronounced different than in the English word "make" meaning create^*. It is pronounced as in "maki", the sushi roll. So it sounds like the two words "maki maki" instead of "make make" as two words.

Is that something based on the pronunciation of English words, or maybe just the way the specific name is pronounced, unrelated to the English language?

In the second case it would not be possible to find the pronunciation based on the language. I think it would not even be possible to find out that it is pronounced different from "make make".

So, is it pronunciation of Makemake just unrelated to English?

The "Makemake" is the last mame of the list in https://www.youtube.com/watch?v=CzJIWxplAbQ&feature=youtu.be&t=9m51s

Spelling and pronunciation are not very closely related in English. Some people on this site would say that they are completely unrelated, but that is a simplification. There are connections, and while some connections are only historical, some continue up to the present day (if I invent a new word "flebbergrat", you'd have some idea of how to pronounce it just from viewing the spelling, without ever hearing it spoken aloud). However, the complicated connections that exist between spelling and pronunciation in English aren't sufficient to tell you the number of syllables in a name spelled like "Makemake". That spelling by itself is ambiguous with regard to pronunciation: you need to know other information aside from the spelling to find out the pronunciation.

Spelling

The origin of the spelling "Makemake" is unrelated to English. The name "Makemake" is taken from the language Rapa Nui.

In English, words or names borrowed from other languages written with the Latin alphabet often retain their original spelling (ignoring the possible dropping of diacritics, change of capitalization conventions, or conversion of letters beyond the familiar set of 26 to one of the 26 from A-Z).

Since Rapa Nui is written in the Latin alphabet, and "Makemake" has no diacritics or unfamiliar letters, the spelling of the name was just taken into English without any changes.

Pronunciation

The pronunciation of Makemake in Rapa Nui would be broadly transcribed in IPA as [ˌmakeˈmake] (I'm basing this transcription on the name's spelling plus the information on Rapa Nui phonology given in Paulus Kieviet's Grammar of Rapa Nui, sections 2.2.1, 2.2.2, and 2.4.1).

The English pronunciation is variable. Spelling is more uniform than pronunciation: it's easy to find one-to-one correspondences between the letters used in written Rapa Nui and the letters used in written English, but it's often harder to determine correspondences for sounds used in different languages. And English speakers often find it harder to pronounce an unfamiliar sequence of sounds than to write an unfamiliar sequence of letters.

And aside from these issues (which affect the pronunciation of borrowed words in all languages) the spelling does not unambiguously indicate the pronunciation of the name in English, as I mentioned in the first paragraph of this answer, so people who have only seen the name written down have to guess at how to pronounce it. Because of the way the name entered English, many people are likely to have first been exposed to its spelling.

The three pronunciations listed in the Wikipedia article are "/ˌmækiˈmæki/, /ˌmɑːkiˈmɑːki/ or /ˌmɑːkeɪˈmɑːkeɪ/". Your description ("pronounced as in "maki", the sushi roll") sounds like it corresponds to the second pronunciation in this list. Explaining these pronunciations in detail would take a lot of time. My attempt at a brief explanation for why some speakers use /ˌmɑːkiˈmɑːki/ would be as follows:

• The spelling "e" is ambiguous; it can correspond to /i/ in word-final position, as in "simile" or "maybe". So the spelling doesn't clearly exclude a pronunciation with /i/.

• Many English words end in unstressed /i/; relatively few English words end in unstressed /eɪ/. In some words, /i/ seems to have developed as a reduced pronunciation of unstressed /eɪ/. So an English speaker might find a pronunciation like /ˌmɑːkeɪˈmɑːkeɪ/ a bit more "difficult" either to perceive or to produce accurately.