> And if I want to have more than one language on the same webpage?

Simple, add more than one lang="" attribute. You can add them to _any_ HTML tag.

Learn more about lang in HTML here: https://html.spec.whatwg.org/#the-lang-and-xml:lang-attribut...

And it can be really useful for styling purposes too - you can use CSS to style writing direction, font, text rendering settings, even which types of quotation marks to use for each language you want to specify

Learn more about :lang() in CSS here: https://drafts.csswg.org/selectors-4/#the-lang-pseudo

Or see an example of how it can be put to use here: https://github.com/mozdevs/cssremedy/blob/master/quotes.css