Swahili is possibly the most famous of the Sub-Saharan languages (ignoring English and French) and is also the most widely spoken with up to 140 million speakers, although the number of native speakers is significantly less. It is spoken to varying degrees in 8 different countries (Map). It is a member of the Bantu sub-family (Map - in pale green) which itself is part of the huge Niger-Congo family (Map - purple).
However, it has lost several characteristics common to Bantu languages, such as tones, and has developed independently under a massive influence of Arab trader communities. As such, I believe this is one of the easiest African languages to learn, especially if you already know some Arabic vocabulary, and could be a stepping stone to learning further African languages.
It's worth mentioning that Swahili is currently being pushed as the official language of Tanzania and Kenya and, in an attempt to form some kind of European-style homogeneous national community, Swahili is replacing many smaller, local languages . Such linguistic imperialism is tragic, but should not turn one away from the idea of learning such a great language.
One of the seemingly more complex aspects of Swahili is the fact that it has 16 noun classes, including separate plural classes, which are somewhat comparable to genders in other languages. Unlike genders in Spanish or German, etc., the noun classes are not random. So the first class (M-) is only animate nouns, such as mtoto meaning child. There are animate nouns in other classes, but they (almost) always have adjectival and verbal agreements according to the M- class. The plural is made simply by changing the M- to WA-, eg. watoto - children.
The most simple class is the 7/8 or KI- / VI- class. This class tends to denote things (kitu - thing) or 'artefacts' (kiti - chair), but is also commonly used for the diminutive nouns (kijiji - village, cf. mji - town). It is the most simple because all agreements are KI- in singular and VI- in plural (sometimes CH- or VY- before vowels) which is not the case with the other classes.
By far the most common class is the N- class (ndoto - dream, mbwa - dog) which incorporates almost all loan words and cannot be recognised by the initial letter since most of the words don't start with n-. The plural form is the same as the singular and can only be seen in the demonstratives or verbs, but not adjectives.
Examples of agreements:
mtoto mfupi anacheza
child short is-playing
The short child is playing.
kiti hiki kimevunjika
chair this is-broken
This chair is broken.
Napenda bia hii
I-like beer this
I like this beer.
Napenda bia hizi
I-like beer(s) these
I like these beers.
There are quite a few tenses, but they shouldn't prove to be too much trouble for an English speaker, although the three simple present tenses can be confusing. However, it is very interesting to see how tenses and subjects/objects are shown in the verbs. Whereas in English the tense can be shown by adding to the end of the word (play > played) or by changing the word entirely (go>went), and the subject usually comes before the verb with the object after, Swahili includes all of this information in the verb, but before the root itself. Eg.:
subject (I) tense (past simple) object (you sg.) stem (see)
I saw you.
This isn't as difficult to get used to as one might expect, but you do have to remember the correct tense markers which is made slightly more challenging by the fact that they can change in the negative form. Eg.:
I didn't see you
(the negative 1st person subject marker is si-)
Another interesting aspect of the verbs is the relative infix, although it only exists in the simple past, present and future (with a slight change) tenses. There is another form which can be used for all tenses. Eg.:
Mtoto aliyeandika barua.
relative marker (M- class)
child who-wrote letter
The child who wrote the letter.
Barua mtoto aliyoianduka.
relative marker (N- class)
object marker (N- class)
letter child that-he-wrote-it
The letter (that) the child wrote.
Lastly, I want to show how Swahili has adopted some words. A lot of words from English are simply taken into the N- class and probably given an extra -i, such as wiki - week, betri - battery. Many Arabic nouns are put into the N- class too, eg. binadamu - human (lit. son of Adam), kanuni - rules (قانون), also, interestingly enough, several words of Persian origin can be found, like bustani - garden.
That said, not all borrowed words are put into the N- class. The word kitabu meaning book comes from the Arabic kitaab, but since it begins with ki- like nouns in the KI- class it is considered to be one of them, even taking the VI- plural: vitabu, despite the Arabic plural being kutub. A similar occurrence happened with the word mwalimu meaning teacher and coming from the Arabic word mo'allem. Since this word begins with m- and denotes an animate object, it was put into the M- class and thus the plural is walimu - teachers. Again the Arabic plural system doesn't work like this.
Obviously there is a lot more to the language than I can write here, but these are some of the parts that interest me. For more information, the Wikipedia article is very good. I intend to make a post glossing a piece of Swahili text in the future for further reference.
1. ojs.ub.gu.se/ojs/index.php/modernasprak/article/download/1187/1026 (PDF file)