Do i put foreign characters on a PFF2 form?

Hi, my father's first name and place of birth both have a Polish letter (Ł) in them. We usually just put an L instead, but it sepcifically states 'Place of birth - name of town or village exactly as it appears on your birth certificate or passport). We're printing it off and sending it, so I'm worried it'll be unclear that the letter is supposed to be foreign. Do we just write 'L' (essentially an English equivalent) or 'Ł'