This post is part of the sub-series on Translating a ClassicPress plugin which is part of the Translating a ClassicPress plugin series.
Internationalization (often abbreviated as i18n as there are 18 letters between the letters i and n) is the process of developing a plugin so it can easily be translated into other languages.
Localization (often abbreviated as l10n as there are 10 letters between the letters l and n) is the process of translating an internationalized plugin.
If you are a theme or plugin author, you should regard internationalization (i18n) and localization (l10n) as a requirement for your ClassicPress projects.