You can choose a tour language from two different locations:
In the creation and editing phase of a product tour
Using the tour builder, when finalizing a tour creation or a tour edit, in the Tour Finalization window, you can choose what language the tour should run in.
In the Tour Options
You can click on a Tour from the Product Tours tab, and under the Options tab, you will find the Tour Language options. You can choose a language from this dropdown list.