Garbled Text
Garbled data was found after importing a normal dump file. After doing some inspections, I found there's NLS_LANG environment variable for user oracle in the source database server, but no NLS_LANG in the target server.
Default Character Set of Sessions
Since there's no NLS_LANG in the target server to set compatible NLS parameters, the import session will use the default character set US7ASCII to convert the dump file. That's why we saw garbled text after import.
Before going further, I think you should know more about NLS_LANG, How and Why.
Import without NLS_LANG Setting
Let's see the log of the import job without setting NLS_LANG:
Connected to: Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
Export file created by EXPORT:V09.02.00 via conventional path
import done in US7ASCII character set and UTF8 NCHAR character set
import server uses AL32UTF8 character set (possible charset conversion)
export client uses UTF8 character set (possible charset conversion)
export server uses AL16UTF16 NCHAR character set (possible ncharset conversion)
...
As you can see, US7ASCII character set was used to convert the data.
Solution
The solution is easy, just set NLS_LANG environment variable for your OS account so as to match the character set of your dump file. For instance:
[oracle@ora12c ~] export NLS_LANG=AMERICAN_AMERICA.UTF8
[oracle@ora12c ~] echo $NLS_LANG
AMERICAN_AMERICA.UTF8
[oracle@ora12c ~] imp \"/ as sysdba\" parfile=SCHEMAS.par
...
Now we can continue our importing job. Please note that, we use "/ as sysdba" via OS authentication to perform the import job. We escaped the double quotes in the command line.
Import with NLS_LANG Setting
Let's see the log of the import job with setting NLS_LANG:
Connected to: Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
This time, UTF8 character set was used to import data.
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
Export file created by EXPORT:V09.02.00 via conventional path
import done in UTF8 character set and UTF8 NCHAR character set
import server uses AL32UTF8 character set (possible charset conversion)
export server uses AL16UTF16 NCHAR character set (possible ncharset conversion)
...
For more globalization support on Oracle, please check Oracle 18c Database Globalization Support Guide: Setting Up a Globalization Support Environment.
As for NLS_LANG, you may check Oracle NLS_LANG FAQ. I believe most of your questions have answers there.
Further reading: How to Change Database Character Set