It's all Greek to your unpublished pages

Recently, a number of concerned publishers have let us know that they're seeing ads in foreign languages in the 'preview mode' of their HTML editors or on pages that haven't been published to the web. We'd like to reassure you that this is normal.

Before our system can display targeted ads on your pages, our crawler first needs to access your pages. While you're building your pages within your HTML editor, your page hasn't yet been crawled, so you may sometimes see less-targeted ads or even ads in foreign languages. However, after you've published a page to the web, you should start seeing ads in the appropriate language. Please also keep in mind that it can sometimes take 1 to 2 weeks for our crawler to revisit your site after you've made any changes, but your ad relevance should improve over time. As always, we appreciate your patience as the crawler continues its work.

Source: Google Inside AdSense Blog