Bug reason
==========

New inventory items get names like "New Script", "New Undershirt" etc., but the names are translated on-the-fly (see EXT-5839), so the user actually sees "Nouveau script", "Nouveau débardeur" etc., respectively.
However when the user changes viewer language, the old localized names still exist in the inventory cache, so, for example, if you create an undershirt in French and then switch to Enlgish, the undershirt will be named "Nouveau d bardeur", which is the old cached localized name with non-ASCII characters replaced with spaces.

Fix
===

To get rid of obsolete translations I clear all caches whenever viewer language gets changed.

Other changes
=============

- Added a check for agent region being NULL to LLAgentLanguage::update().
- Removed LLAgentLanguage constructor and base classes because it's never instantiated.

Reviewed by Seraph at https://codereview.productengine.com/secondlife/r/744/

--HG--
branch : product-engine