"I can tell where they're from without hearing them speak."
"I can tell where they're from just by looking at them."
"I can tell where they're from without hearing them speak."
"I can tell ~”「〜わかるんです」"I know ~" も言えます。
"where they're from" 「どこから来た」・「何人か」"their ethnicity" 「何人か」も言えます。
"without hearing them speak" 「声を聞かずに」・「喋らずとも」"even if they don't speak"「喋らずとも」 も言えます。
[喋らずに](https://eikaiwa.dmm.com/uknow/questions/135295/)についてもっと詳しく知りたい方はクリックしてください。
I can tell where they're from just by looking at their faces.
ご質問ありがとうございます。
・「I can tell where they're from just by looking at their faces.」
（意味) 喋らずとも顔だけで何人か分かるんです
<例文>I can tell where they're from just by looking at their faces. For example, he looks Japanese
<訳>喋らずとも顔だけで何人か分かるんです。たとえば彼は日本人に見える。
参考になれば幸いです。
オーストラリア 
アメリカ合衆国 
