I held back my voice and cried so that the people around me wouldn't notice.
I'm sorry for your loss.
"周りに気づかれないように、声を殺して泣いた" は英語で
I held back my voice and cried so that the people around me wouldn't notice.
といえます。
ほか
"周りに気づかれないように、声を殺して泣いた"
I held back my voice and cried so that others wouldn't notice.
I suppressed my sobs/cries so that no one would notice.
I cried without making a sound so that the people on the train wouldn't notice.
I cried silently so nobody around me would notice.
ご質問ありがとうございます。
「周りに気づかれないように」=「so (nobody) around (me) would notice」
「声を殺して」=「kill (my) voice」
「泣いた」=「cried」
直訳すれば「So nobody around me would notice, I killed my voice and cried.」となりますが、「kill my voice」は英語で言いません。
代わりに「silently」=「静かに」を使います。
例文:
While I was in the train, I heard someone passed away. I was devastated, but I cried silently so nobody around me in the train would notice.
電車の中で訃報に接しました。とても悲しくて、周りの人たちに気づかれないように、電車の中で声を殺して泣きました。
ご参考になれば幸いです。