Error trying to change language
I would check your MySQL permissions - my guess is that you lack the CREATE VIEW permission, which is necessary for multilingual installs. Here is a full list of MySQL permissions needed.

If you go to CiviCRM's Administer menu » System Settings » Debugging and Error Handling, you can turn on Debugging and Backtrace, which will give you a longer error message detailing exactly which permission is missing.  If my answer doesn't fix your problem, please do so, then edit your question to include the additional info.