Multilingual php site Question

Hello, i would like to ask a question, if somebody knows this it would be really helpful to point me to the right direction.

Lets say i am building a multilingual site that when the user selects a language, this is stored in a “language.tmp” file as “ENG” or “SWE”, (might be stupid to ask, but i really dont know) When another user enters the page, what language will he see once the code prompts to “language.tmp” contents?
Will the language remain as set by the previous user or will the code save the setting for each user browsing the site, in the “language.tmp” file?

If somebody knows, please inform.