…

Hello… こんにちは 你好！
en
ar
ja

<button type="button" onclick="document.documentElement.lang='en';return;">en</button>
<button type="button" onclick="document.documentElement.lang='ar';return;">ar</button>
<button type="button" onclick="document.documentElement.lang='ja';return;">ja</button>

body:lang(en) { font-family: sans-serif; }
body:lang(ar) {font-family:Georgia; }