Choose the language of an embedded page or form
An embed sits inside your own site, so it can speak that site's language. Pick one of the page's languages for it, or let it follow each visitor's browser.
One embed, one language
The Embed on your site block of a published page's Overview tab gains a Language choice when the page exists in several languages. Pick one of the page's languages and the snippet points at that language's own address, so the form or the whole page appears in the language of the site it sits on. Left untouched, the snippet keeps embedding the original version.
Or the visitor's browser language
Choose Visitor's browser language and each visitor sees the language their browser speaks, when it is one of the page's languages. Everyone else sees the original version.
Your standalone page never switches language on its own: every language has its own address, for search engines and shared links alike. An embed is never indexed and sits inside your own site, which is why it can follow the browser.