When you change the language the text is much longer so it breaks to the next line. Once it breaks to the next line it pushes all the rest of the page out of position because the rest of the page snags on the floated element that has wrapped.
If you make sure your content wrapper is cleared then at least the content will be align properly although the menu will still be on two lines.
padding: 10px 0;
There's not much you can for the top menu other than changing the design so that it can wrap or make sure items that don't have a drop down are at the end of the line and can wrap to a new line when the language is changed.