LaTeX.css prefixes elements with a class name of
theorem, definition, lemma or proof with a
corresponding label. They are in English by default, but it is possible
to change it to a
supported language,
by setting the lang attribute to the desired language code
and importing the corresponding language file (<link rel="stylesheet" href="https://latex.now.sh/lang/[lang].css"
/>) in addition to the main stylesheet.
Here is a quick demo demonstrating LaTeX.css' language support. If want to support a language that isn't listed here, feel free to open a PR/issue on GitHub.