I use TYPO3 6.2 and the Extension shariff. The default language of this extension is english, but the buttons are always translated to german. My website is multilingual (en, de). The Buttons are included via backend for both languages. How could I define the language per content element "Shariff Social Icons"?
Please clarify your question a bit. What do you mean by "language per record"?
The language is detected automatically from the language configured for the current page. So it automatically adjusts if the language is changed.
See also: https://docs.typo3.org/typo3cms/extensions/rx_shariff/Installation/Index.html#fluid-view-helper
If you need to set a language manually you can do that via the data-lang attribute.