L and Ł are different letters and have tottaly different spellings. I know that for people who doesn't know polish they might be the same but trust me they are not.
Yes, it is the same with a vs. ä and o vs. ö in Finnish and other languages using them (also u vs. ü in German and Estonian). Two dots above the letter mark that the vowel is front, not back. They are different phonemes and there are minimal pairs like Finnish "pelata" 'to play' vs. "pelätä" 'to be afraid'.
Even if I know the rule, at first it was somewhat surprising to find Finnish Äänekoski among cities that start with A or Swedish Örebro with O. But I understand that you easily drop the diacritics you don't use in your own language, as I myself always write "Zelezny" and so on.
Even if I know the rule, at first it was somewhat surprising to find Finnish Äänekoski among cities that start with A or Swedish Örebro with O. But I understand that you easily drop the diacritics you don't use in your own language, as I myself always write "Zelezny" and so on.