Internationalization of bbPress installer

[momo360modena]

For translate installer in french, i must hack the file install.php

Any way to improve this process ? See patch :)

The patch won't work effectively because BB_LANG is never written during install.

I'm working on a language selector which can detect if any languages are available and then allow live switching to that language.

I'm not far from finished solution for this.

If languages are detected at the start of the installation process then they will be made available for selection on the welcome screen. Once past the welcome screen, the selected language will be maintained for the rest of the install process.

Language can now be selected based on the same detection routines in step 1 of the installer. Setting the language in step 1 will not change the language used for the rest of the install process.

(In [1370]) Multi language support for installer.

Installer will now detect the existence of language files in BB_LANG_DIR and return the option on step zero to select a language to use during installation.

A language can also be selected for the installation independently from the installer language. So a person can install a foreign forum in their chosen language. A true "border" case. Boom-tish.

Also contained in this commit is the long awaited RTL installation CSS.

Fixes #839

(In [1371]) Remove error_log() call from last commit - See #839

(In [1372]) Language support in installer - See #839 - branches/0.8

Thank you :)