I was expecting "mmekwisha(ku)la" here.. any particular reason they're separate? In the grammar notes it didn't treat -kwisha as a separate verb, rather an infix.
the -sha- infix actually comes from the verb "kwisha" which may not have been well explained in the lessons, but it can be separated in practice.
You are right. It should be writen together - mmekwishakula. ( Using conditonal forms the monosyllabic verbs hold usually the forms of infinitive )
But...... Looking at this sentence in kiswahili I suppose it is used another construction. In this case the english translation is wrong. The verb " kukwisha" means - to finish, to end. Mmekwisha kula - you ( all) have finished to eat. In this case the sentence should be translated - You ( all ) have finished to eat the lunch.
So, does that mean "Mmeishakwisha" would translate as "You (all) already finished"?