While there are several iOS translation apps that you can get from the Apple App Store, this feature actually comes built-in with iPhones, and you can access it at any time.
You can access the translation feature on devices running the latest version of iOS by locating the Translate app on the home screen and tapping on the icon to launch it.
Select the Camera tab in the app and choose the two languages to translate. Then, use the camera's viewfinder and tap the shutter, or the select photo icon and tap a photo.
Apart from the Translate app, you can also use the iPhone's Camera app to produce translations when using a supported model like the iPhone 14 or iPhone XS.
To do so, point the viewfinder at the text, and a yellow box should appear around the detected text. Drag your finger on the captured text to select and then press translate.
You can also launch the Photos app and pull up an image that contains text from your camera roll. The translate button should appear in the bottom-right corner of the picture.
Certain iPhone apps on devices using iOS 15 and newer also let you select text and translate it into a chosen supported language. These apps include Safari and the Mail app.
For apps that support this feature, just long-press the text you want to translate. Afterward, tap Translate or tap the right arrow to see more options.