Lina's struggle with her elocution is merely another restatment by the film of her inability to sing. It is voice as song that is legitimated by the film, and Kathy's status as the 'right' girl for Don is established by the fact that she can sing. Throughout Singin' in the Rain musical skill is equated with moral good.
The severity of the elocution teacher is also appropriate as these classes are presented as a constraint of the voice, a (careful) speaking rather than (joyous) singing. This is reitereated by Don, who is happy to politely follow the lead of the severe and ascetic teacher until Cosmo's arrival.
It is Cosmo who mocks the teacher, and eventually produces this image of authority abanadoned, of an energetic chaos.
Created in 1998 by Adrian Miles, details, republished 2006.