Delete unwanted language files to free up memory and make your iPhone faster, follow these steps very thoroughly and if you’re not sure what you are doing, my advice is do not try this.

These scripts will back up your language files (except English and Japanese) and will delete all language files except English and Japanese.

Make Sure you set your iPhone to Never sleep!

Step 1) SSH into your iPhone with root access (puddy is a good windows ssh program)

Step 2) mkdir /private/var/stash/langBackup/

Step 3) cd to your /private/var/stash/Applications.whatever programs dir

Step 4) Copy and paste this into your ssh program and run it:

for file in `find . -type d -name “*.lproj” -not -iname “en*.lproj” -not -iname “ja*.lproj” -exec echo {} ; | sed -e ‘s/.///’`; do tar -rf /private/var/stash/langBackup/langBackup.tar ./ ; done

This will back your languages in a tar file located here /private/var/stash/langBackup/langBackup.tar PLEASE VERIFY THIS FILE BEFORE DOING THE NEXT STEP. (should be around 10-15 megs)

Step 5)Copy and paste this into your ssh program and run it:

To back up files:

for file in `find . -type d -name “*.lproj” -not -iname “en*.lproj” -not -iname “ja*.lproj” -exec echo {} ; | sed -e ‘s/.///’`; do tar -rf /private/var/stash/langBackup/langBackup.tar ./ ; done

To remove files:

for file in `find . -type d -name “*.lproj” -not -iname “en*.lproj” -not -iname “ja*.lproj” -exec echo {} ; | sed -e ‘s/.///’`; do rm -vr ./ ; done

This command will delete all language files except English and Japanese.

These scripts can also be run in your /private/var/mobile/Applications dir to remove languages from 3rd party app store apps. Please NOTE: some 3rd party programs are using spaces in their directory names. These scripts will NOT work on those apps. (will not back up them, but also should not delete their language files)
I have also tried these scripts on /System/Library directory. The back up takes a long time around 15-20 minutes. But deleting is Fast! (carrier bundles, quick time and a few other directories are not backed up/deleted do to spaces in the names)

Please use and modify as you see fit and do at your own risk.

Source: Modmyi.com forums