Just posting this for anyone who is facing a similar problem to mine.
This basically atleast avoids the end user from the reset of the language everytime you have to restart zdesktop.
The reasons for the same could be as follows
- Vista Issues. Options are not getting saved due to write permissions
- ZDesktop somehow is not able to write the same in the settings xml file
Resolution
Open the following file Zimbra\zdesktop\conf\attrs\
zimbra-attrs.xml.
This file is stored in the Zimbra settings folder
Search for "zimbraPrefLocale"
Insert a tag within the tag <attr ....> </attr>
as shown below
<defaultCOSValue>en_US</defaultCOSValue>
Restart the appication with the new language set as default
The user locale is now saved and will now be available on the application.
This resolved my issue Hope it does yours too