Oracle Reports Language changes from English to some other

1.     Open report builder => Tools => File Conversion

2.     Select rdf file which need to covert first

3.     Select file path and give any file name on that file, rex file will generate on that path.

4.     Open that file in any editor.

5.     Replace charset = 178 or charset = 0 or any charset datatype length with charset = 31 and save it.

6.     Again open report builder => Tools => File Conversion.

7.     Select rex file first and then open rdf file for file conversion.

8.     Save rdf file

Check the report if not correct result follow below mention action plan.

Problem: All customized reports giving output in English language got disturbed. They are changed from English to some other language.

Solution: Kindly check the report log file. It might be displaying error:
REP-0004: Warning: Unable to open user preference file

Request Logs Contain the Message "REP-0004: Warning: Unable to open user preference file" (Doc ID 1120529.1)

Copy the prefs.ora file from /opt/oracle/apps/tech_st/10.1.2/tools/admin to /home/oracle/ 

Copying " pref.ora file to /home/oracle." would be required if all requests are failing to Print. If you remove pref.ora file and print Active users report and that works then you do not need this. Having prefs.ora being present at /home/oracle has no harm. It is just a preference file. 

Bounce the application node and retest if the issue is resolved. If above solution doesn't work then after taking backup of existing environment file and add the below lines and bounce the application node and retest. It must be resolved by now.

"IX_PRINTING=$FND_TOP/$APPLRSC/ixlib.cfg 
export IX_PRINTING " 

The note might be useful Oracle Reports 10.1.2 NLS Setup Guide for Oracle Applications Release 12 (Doc ID 415967.1)