The Fiji official language is actually more than one language. When you visit this part of the world, you will hear the locals speaking English, Fijian, and Fiji Hindi. All three of these are considered the Fiji official language and none of them are higher ranking than all the others.
However, when you are speaking of the Fiji national language, that is considered English. When you are visiting these islands, you may also hear a few people speaking Korean or Chinese. Therefore, those are also considered Fiji languages.
English has been part of the Fiji language since the first explorers and traders arrived on these islands. However, the English used back then is very different than the English used as the Fiji national language today.
You may be wondering why Fiji has Hindi language. This is the language that is spoken by the locals who are of Indian descent. Their version of Hindi has been derived mostly from Awadhi and Bhojpuri varieties, but it is also filled with a few words from the English and Fiji language.
Those people who speak Korean and Chinese in Fiji are people who have moved to the islands. Most of these people are migrant farmers and they are quickly learning the other Fiji languages.
There are a few other languages spoken in Fiji, so do not be surprised if you hear a few Polynesian and Micronesian languages interspersed into your days.
Basically, you never need to worry about whether or not you can communicate with the locals when you travel to Fiji for a vacation. Almost everyone speaks English, and those that do not speak it fluently still know enough to carry on basic conversations with you. So, embrace the fact that English is the Fiji national language and simply learn a few words from the other Fiji languages just in case you want to fit in with the locals a little more.