BeanDoc mostly consists of values read directly or inferred from your Spring XML files and thus will reflect whatever language you wrote those descriptions and identifiers in. It also uses some static labels and these can be in any language that we have a translation file for - you just specify the locale as an option in your beandoc.properties file.
We're always looking for additional translations since they're easy to add to the source tree. Our current set can be seen here
If you can translsate the default English set into a language we don't already have, please do so and add an item to our tracker so we don't lose it.