Ну и в догонку - помимо второй у гайда есть еще третья глава , сфокусированная на клиенте, где вендор продублировал послание ленивым и занятым:

Database Globalization Support Guide
3 Setting Up a Globalization Support Environment
Choosing a Locale with the NLS_LANG Environment Variable Should the NLS_LANG Setting Match the Database Character Set?
The NLS_LANG character set should reflect the setting of the operating system character set of the client. For example, if the database character set is AL32UTF8 and the client is running on a Windows operating system, then you should not set AL32UTF8 as the client character set in the NLS_LANG parameter because there are no UTF-8 WIN32 clients. Instead, the NLS_LANG setting should reflect the code page of the client. For example, on an English Windows client, the code page is 1252. An appropriate setting for NLS_LANG is AMERICAN_AMERICA.WE8MSWIN1252.

Setting NLS_LANG correctly enables proper conversion from the client operating system character set to the database character set. When these settings are the same, Oracle Database assumes that the data being sent or received is encoded in the same character set as the database character set, so character set validation or conversion may not be performed. This can lead to corrupt data if the client code page and the database character set are different and conversions are necessary.