Where are you changing the language?
Are you trying to change the language of a user or for the project.
Changing the language for the user will only take effect after the user logs out and back in again. I think there is a module in the market place that allows for switching the user language without the logoout an login. If this is the case then have a look at tat module.
If the issue is in changing the language in the project, some more details are needed as I don’t understand what you mean with the problem being related to a time delay?