Definition
A standardized representation of text
Unicode

How does it work?

The world has hundreds of writing systems: latin, chinese, arabic, devanagari, etc, etc. Unicode was designed to catch all of these in a single format. Each character is represented by a code point and stored in one of several "encodings", of which UTF-8 is the most popular one.

An example:

1997-07-16T19:20:30.45+01:00

When should you use it?

When your application is used by users with different writing systems.
If your application has only a very limited user group, a specialized encoding (such as Latin-1 for Western Europe) could be used, but the gain is minimal and converting to Unicode later can be a hassle.
The choice for Unicode is basically a no-brainer.

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