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...
Merge branch 'fix-localization-cache' of https://github.com/mlocati/concrete5 into mlocati-fix-localization-cache
Merge branch 'mlocati-fix-localization-cache'