Currently, 1Blocker is available in two languages: English and Russian. You can switch between these languages by changing their priority in the iOS/macOS settings.
On iOS, you will need to go to iOS Settings app > 1Blocker > Preferred Language.
On macOS, it is necessary to go to macOS System Preferences > Language and Region > Preferred Languages. If Russian has a higher priority than English, 1Blocker's interface will be in Russian. To change that, just put English before Russian in the list of languages.
After that, you will need to restart 1Blocker, so that it can check the language and change it.