Oracle SQL Developer client encoding

On the PC that PLSQL is installed, set the value of NLS_LANG registery entry equal to the PC's operation system locale (code page), equivalent value.

How to detect operating system language locale?
How to map OS locale to NLS_LANG value?

When using PLSQL the initial parameter of client-language that is required to create an Oracle session is read from NLS_LANG registry entry.

Due to Oracle documents, invalid data usually occurs in a database because the NLS_LANG parameter is not set properly on the client.The NLS_LANG value should reflect the client operating system code page.
For example, in an English Windows environment, the code page is WE8MSWIN1252. When the NLS_LANG parameter is set properly, the database can automatically convert incoming data from the client operating system to its encoding.

When using JAVA method, the client-language parameter is set by the value from the Control Panel, under Regional and Language Options, so the things will be OK.

You can try to change NLS_LANG value on your Win PC with regedit tool.

Path is: \HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE, when NLS_LANG contain value of your Oracle client's current encoding.

There is Oracle's list of available encodings:Commonly Used Values for NLS_LANG