Akan is one language with several names, and which name a speaker uses depends on where they are standing. Asante Twi is the variety of the Asante heartland around Kumasi. Akuapem Twi is spoken on the ridge north of Accra. Fante is spoken along the coast. The three are mutually intelligible, and a speaker of one follows the others without difficulty, but each has been given its own written standard, so that Akan has three orthographies and three bodies of printed literature rather than one.
That happened because writing came with missions, and different missions worked in different places. Akuapem Twi was standardised first, by Basel mission scholarship in the nineteenth century, and it became the language of the Akan Bible; the Methodists worked on the coast in Fante; Asante Twi was standardised later and is now the variety with the most speakers.
The language is Kwa, in the Niger-Congo family, and it is tonal. Vowel harmony governs which vowels may appear together in a word, and the written standards mark it with additional letters that English keyboards do not carry, which is one practical reason Akan is often written online without them.
Akan is the first language of a large plurality of Ghanaians and is used as a second language by many more, so that it functions as a national lingua franca in a country whose official language is English. It has no historic script of its own; the writing systems in use are Latin.