Hi New User,
Thank you for contacting Telerik Support.
1) The languages available in the dropdown of this control are populated from the languages you have enabled in your website web.config:
"en, es, fr, de, bg"
You can add whichever culture you want to enable localization for.
2) Sitefinity Navigation controls are bound to a SiteMap datasource. This means that they will automatically get appropriate language versions for each page once a page is created for a specific language.
3) The navigational button text comes from the Menu Name property for each language version of a page. This means that it is automatically populated for that specific language version.
For more information on localization in Sitefinity I will advise you to take a look at our localization webinar: Multi-Language & Localization Support in Sitefinity
the Telerik team