Ok looks like we need to do a hard-reset
1.Power the phone off.
2. Hold down the following three buttons (Volume UP, Power, Home)
3. Release the buttons after the Android logo appears
4. Use the down key to select 'Wipe Data\Factory reset' (fifth option from the top)
5. Then press the power button
6. Select the option to confirm reset, which is the option with the most text.
7. Press the power button
The phone should then restart and take you through the settings as if it was brand new and let you chose your language.
You may wish to watch the video here which shows you the steps required.
Please let me know how you get on, and if you need anything clarified.