Language supplementation is a process where we copy missing translations in a particular language X from existing texts in language E.It is recomended to carry out language supplementation after carrying out any of the below activity :-
a.Importing EHPs
b.Installing a new language.
c.Importing Support Packages.
d. any tranport activity which affect language.

SAP has give the customer choice to define which language they want to use for Supplementation. So may be a customer in Poland selects DE for supplementation of PL because his employees do understand DE too but do not understand EN.

The Language Supplementation has to be started manually from SMLT.

We recently upgraded our system from ECC 4.6 / AFS 3.0 to ECC6.0 / AFS 6.04.And we found that the some functionalities are missing in ECC-6.0 /AFS 6.04 (Grid Value & Category data is not updating in HU overview screen).

we were able to activate the business function set in our development system but were not able to do the same in our production system.

later we found that Due to system change options(SE06) , it is usually not possible to activate business functions directly in a quality system or production system.

The way (suggested )to activate it in QAS or PROD system is that the business function settings should be transported from DEV to QAS and then to PROD(in order DEV-->QAS-->PROD).

A transport request that contains the business function settings of the development system can be generated in t-code SFW5 in the development system and choose transport from menu system setting. After the transport has been generated ,it can be imported to the quality system.

The import of the transport will automatically activate the same business functions that were in the development system when the transport request was generated.

I do not have concrete reason to mention why SAP came up with separation of ABAP and JAVA stack installation (unlike Dual stack installation performed earlier ).

It is evaluated and believed that performance was one of the major reason for it. As of SAP Business Suite 7, you can no longer install Dual Stack Application Systems (ABAP+Java) except for Solution manager and PI .Existing dual stack Application Systems are still supported.

However, new systems should be installed as separated ABAP and JAVA Systems.

If you want to use both SAP Business Suite ABAP and Java Components in your system landscape, you have to proceed as follows:
1. Install a separate ABAP-based SAP Business Suite system.
2. Install the required Java components in a separate Java-based SAP system.
3. Configure the connection of the Java-based SAP system to the ABAP-based SAP Business Suite back-end system.

EHP4 for SAP ERP 6.0, SAP CRM 7.0, SAP SCM 7.0, SAP PLM 7.0, SAP SRM 7.0 are part of suite 7.

There is some work around for BI for which one can refer to SAP note :-
Note 1181025 - NW7.0 EHP1 - Install BI Dual Stack System (Workaround)

If requirement comes to you that business needs a beep sound in RF console when it scans a bar code this is what you should do.

Step 1: Stop laughing
Step 2: Follow note 371838

Suppose we have a standard SAP function module issuing an error message because of invalid input data. Now if we are calling this function module from any custom conversion program and such an error message is issued by the function module, the entire processing would stop and program would terminate displaying this error message. In case of a background job, it would also show an error and abruptly stop.

In order to handle such scenarios, we can provide an additional parameter in the function module exception called 'ERROR_MESSAGE' and give a sy-subrc value to it. This should be before the normal OTHERS parameter.

Now when the error is issued in the function module, the program doesn't terminate immediately. But the SAP function module returns with the SY-SUBRC value corresponding to the ERROR_MESSAGE exception.

Also the error message details can be found in the standard system message fields (SYST structure) and can be used by the custom program to populate any processing log / report.