UnicodeDecodeError when use Oracle DB as secondary db in django 1.8

I wanna use an oracle db in my project which I can't changed because it's from an old project. NLS_LANG in db set to 'AL32UTF8'. When I use only oracle db, set os.environ in every models in apps so code works very good. If I remove this setting got UnicodeDecodeError exception.

But I need to use another db for django users. For test, I decided to use a sqlite db for users. So change db setting and make my default db sqlite (for django users) and another db (called 'secondary') for oracle and wrote a db router for project so I can use all db without problem, but when I wanna use secondary db, got UnicodeDecodeError exception again.

What should I do for make it works?