If I'm creating a custom list in my code, how can I make fields localized, so when user has set e.g. Polish, he can see field names in polish and when he has English language set, he can see field names in English. Could you give some example?
Using Resource File could be a good choice but it won't allow the content editors to enter the tranlations. Chris Brian talk about the language store which is quite flexible and easy to implement and solution is available at codeplex too
You need to use resources. For example you can use this blog post: Using Resource Files (.resx) when developing SharePoint solutions
Have a look at the property TitleResource of your field. Through this property you can set your field names for each culture. MSDN Description of SetValueForUICulture