Translation:Duo keeps helping people learn Esperanto.
Can the person helped also be indicated in the accusative (helpas homojn ...) or is it like German where you just have to know that you essentially help to someone?
helpi al iu fari ion = helpi iun fari ion ?
I wonder if ‘al’ is used here instead because ‘Esperanton’ also has the accusative case, lest there be confusion. Does anyone know?
There are two distinct accusatives here: the direct object one (Esperanton) and the preposition substitution (al). The good rule of redaction is to not use the two types of accusative in the same sentence.