Translation:It is being built
i- = N-class singular (class 9) SUBJECT prefix
-na- = PROGRESSIVE ASPECT (generally PRESENT)
-jeng- = build
-w- = PASSIVE VOICE
-a = INDICATIVE MOOD
The i- essentially stands for "it". The reason the N class is used could be because the noun it's standing for is in the N class ... I'm not sure, but I suspect the N class can also be used as a kind of default, like if you see some weird thing like a flying blob covered in dots and ask "What is that?" I think you'll use the N class for it.
Here, some examples of sentences with the passive extension "wa" (also with verbs concording with different noun classes (chakula and kiswahili, with ki-vi concords, and picha, I think it is in the ma class):
Swahili Grammar: The passive extension "wa"
Note: Also, if you think a construction as a home, the noun "nyumba" is in the n class (inanimate), and verbs agree with the prefix i- in the singular and zi- in the plural.
I have put the prefix for M-Wa nouns in the sentence "Kijapani anakuja." (in a comment before) and someone told is not right because Kijapani (Japanese language) is not human (also this works for some animals), so, to say "Japanese (language) is coming." needs other prefix, "Kijapani inakuja" or "Kijapani kinakuja"; the first is the example that the user told me, and the second is the example I took from the Wiktionary conjugation chart because I think the verb concords with the Ki-Vi noun prefix. I cannot really say that I get all of this and I hope to show not only the information, also I need conclusions about it.
I have just added the entries for "kujenga" and "-jenga" in Wiktionary:
(I have put these taking the source code from the verb "-penda" and the infinitive "kupenda", to love /to like, because I think is regular, then someone else can add information as the etymology or perhaps adding some irregular forms, as in the verb "-ja", to come.)
*# to [[love]], to [[like]], to [[pleasant|be pleasant]]
(And then, changing this to)
*# to [[build]], to [[construct]]
(Note: the asterisk is not needed. So, the Swahili for "build" is now available in the tranlations chart, but the Swahili for "construct" needs to be added. I have put this verb thinking it is valid, but perhaps it still can exist other Swahili translations.) ;)
Aha, now I get you, I think. I got confused when you said prefix, I think you mean suffix, no? The "-wa" suffix indicates passive form.
a-na-jenga = he (present) builds/is building I-na-jeng/w/a = it (present) being built. Does that help?
The verb-roots don´t change depending on class. The prefix,suffix and infix show the different tenses. So it is not like in spanish where the verb changes depending who does something.
That definitely helps, as I was thinking the i- prefix indicated the passive form. No, what really confused me here was that on the hover translation (the little hint you get, if you put your cursor over the word), it said under the translation "(N/N)." That may just be a sort of typographical error, though.