[Closed] I want to set Mexican spanish translation feture for users

Background of the issue:
I want to set Mexican Spanish translation feature for users on my site hidden link. This language is not present in the options; there is just Spanish language. I want users to have the option to choose the language when they visit my site.

Symptoms:
The Mexican Spanish language option is not available in the settings.

Questions:
Which and how to choose the setting for Mexican Spanish?
How can I integrate the language selection feature for users?