If your translated pages appear slower than the original pages, there are a few things you can do.
First, be sure to check where problems are coming from. You can learn how to use Debug Objects plugin and identify performance issues in our FAQ on debugging performance problems.
When you see an unexpectedly large number of queries, go through these potential sources.
String Translation Tracking
WPML lets you see where translatable strings come from. It's a powerful feature, but also resource hungry.
Go to WPML->String Translation and make sure that "Track where strings appear on the site" is not checked. This feature will cause SQL queries for each GetText string in your site. Those queries happen only when you're logged in as Admin.
Auto ID Adjust
WPML can automatically convert hard-coded IDs to the current language. You can control this via WPML->Languages->Make themes work multilingual.
If "Adjust IDs for multilingual functionality" is selected, WPML will perform SQL queries whenever the theme tries to load items with specific IDs. This is often required, but you can optimize it yourself.
You can disable this option and use icl_object_id and other functions from WPML's API, to turn your theme multilingual.