Always enable localization cache

Localization cache is enabled only if the initial locale is not en_US.
But, mainly on multilingual sites, we may have an initial en_US locale, and the final locale is set after the initialization of the Localization library.

So, let's always enable the localization cache...

Bugtracker: http://www.concrete5.org/developers/bugs/5-6-3/localization-translation-parsing-is-not-cached/