I know there is a simple way to change the frontend language by tinkering with the locale folder under app/design/frontend/default/default/locale/en_US for example. Is there any way I can do the same for this theme? I need to translate and implement 3 other more languages.
The translation I want is NOT available at Magento Connect. And uploading it via the directory above also does nothing. Do I have to tinker around with some settings for this theme? In the default theme the translation.csv would implement directly. But with the AccessShop theme, this is not the case. Where can I add a custom translation and how do I set this?
No there is nothing you need to do specific in this theme for the language. It is same as for other default settings.
If you can set up the language settings for default magento then it will surely work with our theme.
Check how to create multi-language store in magento first.