Swahili to English

-shenzi is a noun or adjective root meaning uncivilized, ucultured, uncouth, or even filthy (mshenzi, as noun or adjective, means an uncivilized or uncouth person).

Its invariable use today is as an insult; in the 19th Century Arab and Swahili traders described themselves as Wangwana (civilized people) and upcountry Africans as Washenzi. In the Congo the dialect of Swahili used there is still called Kingwana, Although Swahili (Kingwana) is the native language of virtually all eastern Congolese, few of them are familiar with the word "Swahili."

This appears to be a mistake made by someone who uses Swahili words from the dictionary without understanding how they're used. The form of this word is a verb, but its root, ustawi, or usitawi, is a noun and cannot be declined as a verb.

The noun usitawi means "flourishing" or "in good condition." The verb is kusitawi (kustawi), but this contributor has never heard it used of human beings but only of crops, plants, or possibly livestock. Mahindi yangu yanastawi, my corn is flourishing. There are many ways to say "I am in good condition" (which appears to be what the made-up word naustawi is intended to convey), but common ones are hali yangu nzima, mimi mzima, najisikia mzima, all of which can be translated as "I am in good condition" or "I am well."