If you plan to enter the Polish market, English is not enough. Contrary to what Poles declare, only 30% of them speak English at fluent level.
The Polish-language version of your mobile application increases your chances of gaining loyal customers and regular subscribers. Let me translate your application into Polish, and I will adapt it to the users. They won’t want to stop using your app.
Are you creating a website or a web portal? See my translation and localisation of websites services.