I've got a different country's weather app on my iPhone that I sometimes check.
違う国 - Different country
天気予報 - Weather forecast
アプリを入れる - To install an app、To download an app
たまに見ている - I sometimes check, I check from time to time etc . アプリの場合は see、look や watch はとても変です。 Check が一番自然です。
違う国の天気予報もiPhoneのアプリに入れて、たまに見てるよ - I've got a different country's weather app on my iPhone that I sometimes check / I've installed a different country's weather app on my iPhone that I check from time to time/ I've downloaded a different country's weather app on my iPhone that I sometimes check になると思います。
a different country's weather app - 違う国の天気予報アプリ