Everything you always wanted to know about Oracle Database NLS_LANG and character sets

I have recently come across the Oracle Database Globalization Support again and the question of what character set is used when, how and where. A lot of this can be or is controlled by the NLS_LANG OS environment variable, buried deep down in the Database Globalization Support Guide. But I just found this “hidden gem” on the Oracle web page that, for some reason, isn’t very well indexed by the search engines: https://www.oracle.com/database/technologies/faq-nls-lang.html

I also found that the page could do with an overhaul and a few more details, so I’ve taken the liberty to provide an updated version of it over here: Oracle Database NLS_LANG FAQ

Hopefully, this will help other users of Oracle Database to understand this environment variable better and maybe help to improve the overall search engine ranking for that page. If you have any questions regarding what character set is used or should be used and how to set what, that FAQ page is your friend.