my son is 3.5. he speaks in sentences and communicates well with parents... but he is inconsistent in responding to his name and communicating with strangers and other people.

Question

Accepted Answer

if your child is able to understand and follow all the commands given and is able to you hear what you are saying with proper eye contact then do not worry much about the language skills of the child because speech will gradually come. 
Try to avoid TV mobile laptop like screen time and spend more time with the child talking with the child as well as if more people are available to talk with the child and this will also improve the social and language milestones of the child.  
language skills develops over time

Accepted Answer

See Is your child responding to the name properly when the parents are talking to the child and don’t worry about that see it is just a stranger anxiety that the child is having for almost 2 years kids have been in lockdown which is why a child is not very comfortable in communicating with other people strangers so as your child will start going to the school things will definitely start becoming better