Jenkins displays text depending on the language of the browser. So all you need to do is change the language of your internet browser.
Note that, depending on the browser and on the language, you might need to download addons. For example, for Firefox, see Changing the language pack.
Under Firefox, a tool such as Quick Locale Switcher might help quickly test various languages.
You can additionally change the system language (used when builds are executing), as well as the user interface language for all users by using the Locale Plugin.
See an old example of Hudson in French: