This is now defined in the Language [lang].xml file in the Language metadata settings. If you are having locale problems such as dates do not appear in your language for example, you might want to check/edit the entries in the locale tag. Note that multiple locale strings can be set and the host will usually accept the first one recognised.
Mambots have been renamed as Plugins. Mambots were introduced in Mambo and offered possibilities to add plug-in logic to your site mainly for the purpose of manipulating content. In Joomla! 1.5, Plugins will now have much broader capabilities than Mambots.
The improved Installer can be found under the Extensions Menu. With versions prior to Joomla! 1.5 you needed to select a specific Extension type when you wanted to install it and use the Installer associated with it, with Joomla! 1.5
In Joomla! versions prior to 1.5 there were separate processes for creating a Static Content Item and normal Content Items. The processes have been combined now and whilst both content types are still around they are renamed as Articles for