Five vs seven vowels

[eruedin]

At https://apics-online.info/surveys/60 you write:

4. Phonology and tonology
Kinshasa Lingala uses five vowel phonemes, all of which are oral.

Table 1.Vowels

  | front | central | back
close | i |   | u
close-mid | e |   | o
open |   | a |  

This is absolutely correct in relation to Lingala in Kinshasa (as you mention). However, Kinshasa is only the capital province of the country with around 10 million inhabitants. Even if the remaining 70 million inhabitants do not all speak Lingala, the traditional, rural, literary and classical Lingala spoken in the non-capital town areas should also be mentioned. A second table would be conceivable in addition to the existing one:

Traditional, rural and literary Lingala uses seven vowel phonemes, all of which are oral.

Table 1b. Vowels

  | front | central | back
close | i |   | u
close-mid | e |   | o
open-mid | ɛ |   | ɔ
open |   | a |  

I could imagine a simple two-part table with the existing section on the left and the proposed addition on the right.