Internationalization is preparation that makes localization faster, cheaper, easier or even unnecessary.

Anecdotal evidence from many, many people over the years consistently indicates that proper internationalization reduces the cost of subsequent localization by about 50% and reduces the time needed for localization by about half.
~The Localization Industry Standards Association (LISA)

It is best to fix localization problems once in the source language so you do not need to fix the same problems multiple times in multiple languages.