Localization is feature provided by iOS which translates your app into multiple language.For Localisation,Internationalization is necessary.Internationalization is process of making iOS app able to adapt different culture,language and regions.
Internationalization (i18n) and Localization (L10n) are used to adapt software according to differences in languages, regional differences and target audience.
Internationalization : the process of planning for future localization i.e. making the software design flexible to an extent that it can adjust and adapt to future localization efforts.
Localization : the process of adapting the software to a particular region/country/market (locale).