Fix for language overrides, paths & properties.

- missing additional languages overrides and fallback to default site language overrides;
- incorrect paths to *.ini files;
- incorrect JLanguage properties (fallback to default site language properties).

##### Fix 1
Without line 48 some paths look like this:
```php
[joomla] => Array
    (
        ....
        [D:\XAMPP\htdocs\joomla/language/.ini] => 
    )

[plg_system_logout] => Array
    (
        ....
        [D:\XAMPP\htdocs\joomla/administrator/language/.plg_system_logout.ini] => 
   )
```
This is happening because ```$application->input->get('language');``` is empty or does not exist.

##### Fix 2
Without line 203 the current language is not registered "completly" let's say and the overrides for current language are missing + JLanguage properties (like upperLimitSearchWordCallback, ignoredSearchWordsCallback, etc) fallback to default site language ones.

Everything works now!