It was my first time hearing someone talk in their sleep in a language other than English, and it was rather new to me.
Hearing someone talk in their sleep in a language other than English was rather new to me.
My first time hearing someone talk in their sleep in a language other than English was rather new to me.
rather は「かなり、ずいぶん」の意味なので、rather new で「とても新鮮」ということ。a language other than English で「英語以外の言語」となります。
英訳１：It is/was my first time -ing.は「～するのが初めてです／でした」という意味を表せます。
英訳２＆３：hear someone talk は「～が話しているのを聞く」ということ。
その他の言い方：
- It was my first time hearing someone sleep talking in a language that wasn't English, and it felt so fresh.
- Hearing someone talk in their sleep in a language that wasn't English was a new experience for me.
アメリカ合衆国 
