Support Timezone

What is a timezone?

A timezone is a region that shares the same interpretation of time based on their relative position on Earth to Sun.

Why do we have timezones?

A moment for people on Earth are the same, but people describe the moment differently.  For some people, such as me, who is living in San Francisco Bay Area, the time is 3PM now, but for people living in India, it is 3:30AM in the morning.  Also, timezone change the way how to view their date within the calendar.  For me, it is June 10, 2016, but for people living in Bangalore, India, it is June 11, 2016 already although many of them have not yet waked up.

When people look at the evnts happened in the past or the events should happen in the future, they may want to describes the time.  Time components of a timestamp data helps describing the time when the event happened or should happen.  It is the reason why we need to support timezone.  It helps accurately describing the time.  If you just need to roughly describe the time at the "date" or "month" level, you do not need to mention time zone.

(more)

Identifying the language used in the software

The software you uses may be used by people using other language. A software may be designed to support multiple languages.

One scenario is that the software may be designed to support multiple languages with different versions. You install the version of the software available in a language. If you want to use the software in a different language, you need to install a different version.

A software may allow different user who install it to use a different language, but while you are installing, you need to specify which language you are using. A variation to this scenario is that you can switch the language you want to use even after installation. However, you can only use one language at a time.

Some software allows multiple users and each user can have a different language preference. These users may store their own data in different languages. The software can display different language based on user preference and store the data in different languages. An extreme of this scenario is that the data created by a user can be stored in a language but can be displayed to another user in different language.

In all the above cases, one of the common requirement is to allow the user to specify a language.

How does the language is identified? How does the user tell the system which language they are using?