The french language pack will give you french versions of many of the field values and messages rules, and therefore when you set your locale to french (for instance from the developer portal with the landing page designerStudio > User Interface > Localization Tools > Locale Settings), your ruleset list will be modified such that those french versions of the field values and message rules are picked up.
After you do that, many of the menus and screens you bring up will have their standard phrases showing in french. For instance, the buttons such as "submit" and "cancel" should appear in french.
Now, for the reverse, where you want to produce french content, you can start with the designerStudio > User Interface > Localization Tools > translate to new language landing page, which will let you define your own french versions of rules such as field values and message rules.
Thank you very much for your prompt response. But I still have some doubt so trying to rephrase/elaborate my question a bit more here. Would really appreciate if you can elaborate on that as well.
Say, if we acquire the language pack for French, then is it possible to create Locale settings in such a way that only some specific user, who is still sitting in US, can have the ability to create correspondence template in French language? The point is that particular user should still be able to use the application totally in English language As Is i.e., the requirement to use French is ONLY restricted to this particular functionality of creating a correspondence template.
Hope I am able to explain the requirement more clearly now.