Reference notes:

NLS Frequently Asked Questions (Doc ID 399789.1)
Globalization Guide for Oracle Applications Release 12 (Doc ID 393861.1)
Oracle Applications NLS Release Notes, Release 12.1 (Doc ID 788053.1)
Oracle E-Business Suite Maintenance Procedures. See the Adding and Maintaining NLS Languages section in Chapter 1
Requesting Translation Synchronization Patches (Doc ID 252422.1)


Note : a) Your DB character set should be the one which can understand the installed language character. UTF8/AL32UTF8 are the best character sets for multiple languages as they are the super set of all other character sets.

You can use this SQL command to check the database character set:
select value from nls_database_parameters where parameter='NLS_CHARACTERSET';

b) Deactivating a language is not supported. Even if you are not using them, once activated, you must maintain all languages that are active in an NLS system

c) The minimum recommended space required for each active language in the APPL_TOP is 7GB and 1GB for the database.


Steps


1. From Oracle Applications Manager, go to License Manager and activate or change your base language to a new one. eg : If we want to add Japanese , activare Japanese

Then click on submit


SQL> SELECT language_code||',' FROM fnd_languages WHERE installed_flag IN ('B','I');

LANGU
-----
US,
JA,

2. From AD Administration, run Maintain Multi-lingual Tables (AD Administration Main Menu > Maintain Applications Database Entities Menu). will take around 10 mins

3. Run the Translation Synchronization Patch utility (adgennls.pl). .

Log on to your Applications' administration node as the APPLMGR user and source the APPL_TOP environment file. Use the manifest generation tool to generate a manifest file by executing the following command:

perl $AD_TOP/bin/adgennls.pl

For ex:

$ perl $AD_TOP/bin/adgennls.pl
Please enter the APPS User [APPS]:
Please enter the APPS password: Manifest file generation is in progress...
Manifest generated in: /u01/oracle/apps/apps_st/appl/admin/TEST/out/adgennls.txt

If you open the file, you will see something like

# Release: R12
# Active languages: JA, US
# Manifest generated by adgennls.pl 120.7.12010000.2

ad patch/115/import/US addiag.ldt 120.0.12010000.1 JA:MISS
ad patch/115/import/US addrimt2.ldt 120.0.12010000.2 JA:MISS
ad patch/115/import/US addrpimt.ldt 120.6 JA:MISS

The manifest generated from the tool is located at :

$APPL_TOP/admin/$TWO_TASK/out/adgennls.txt

The manifest contains the files of all your active languages that are currently on your Applications instance. You do not need to run the tool for each individual language.


4. After you generate your manifest, you can go to https://updates.oracle.com/TransSync (use your My Oracle Support username and password).

Provide your email address and upload your manifest file

Follow the instructions on the screen to upload the manifest file. A Translation synchronization patch will be generated specifically based on your manifest for each of your active language. The patch will synchronize the language file versions and American English file versions in your Applications instance. If you select the option to get latest translations, the patch will also bring your translations up-to-date. You will be notified by email when your patch is available for download.

If your current translations are already up-to-date and in sync with your American English file versions, you will be notified by email that there is no need to apply Translation Synchronization patch.

You should receive the email notification within 48 hours. You can also check your request status at https://updates.oracle.com/TransSync.
If you have any question, you may contact Oracle Support for assistance


5. When you are notified that it is available, apply your Translation Synchronization Patch (TSP) for all languages you requested.

We got the R12 Translation Synchronization patch 12823874 for Japanese, which is of size 704 MB.

Bring down the app services before applying this patch

6. Install the Release 12 NLS Help.
In our case we need to apply Japanese help patch 7303031

it will be good if we bring down the apps services & then apply it

7 . run the AD Administration utility to generate message files from the Generate Applications Files menu (took around 2 mins)