After you installed the language, follow the steps below.
Once the BlackBerry Device Software is installed on the BlackBerry smartphone, complete the following:
1. Launch Setup Wizard from the device
2. Select Language and Text Input
3. Select Next
4. Check languages that will be used
5. Select Finish
To change language on Device for Input and/or UI:
1. Go to Options
2. Select Languages and Text Input
3. Select appropriate language from drop down for Language and/or Input Language
You can also view this information at the link below.