Diakrites land wrong in Oracle database
sqlplus inherits the encoding from calling cmd.exe codepage. You must tell Oracle which codepage is used with NLS_LANG value. Value of NLS_LANG and used codepage have to match. 

Try this:

c:\&gt;chcp 1252
Active code page: 1252

c:\&gt;set NLS_LANG=.WE8MSWIN1252

c:\&gt;sqlplus ...


Note, if you run sql-files then ensure they are saved as "ANSI" (i.e. CP1252 for "Western" Windows). If you use a different encoding then set chcp and NLS_LANG accordingly, for example:

c:\&gt;chcp 65001
Active code page: 65001

c:\&gt;set NLS_LANG=.AL32UTF8

c:\&gt;sqlplus ...


See also https://stackoverflow.com/questions/33783902/odbcconnection-returning-chinese-characters-as/33790600#33790600