I don’t know what the backend looks like, but if you have the power to add Polish to your instance’s language list, please take care to write it using lowercase p.

In Polish, unlike in English, adjectives derived from proper nouns are not capitalized. This does apply to the language name.

You could argue that it’s capitalized for aesthetic reasons just like “Undetermined” is, but then I see other languages on the same lists starting with lowercase letters making this inconsistent.