Name the months only in English

[c4]

Hello all
I have a problem with the months names in the osclass. The whole site is in Polish and the names of the months have not translated. In which file to look for month names?

This is not my portal but it's exactly the setting I'm asking for
settings: Date & time format. In this case April 10, 2015 - Which file or setting is responsible for the language of the month?

[dev101]

core.po inside oc-content/languages/*

where * is your language code folder name (e.g. pl_PL)