That's a very strict measure for a human language. Borders tend to be blurrier among words. Are we learning a very specific dialect of Polish and English here? (if so which ones?) Are there no variations of these synonymous words' meanings among 345 mn native speakers?
Are the meanings of beautiful/pretty and ładna/piękna always so distinctive?
It is true that Google Translate (not necessarily the best arbiter) gives "Kadın güzel" for both "the woman is pretty" and "the woman is beautiful". It then added a "çok" for the case of beautiful :-).
Learning other languages does broaden the mind, after all.
I'm puzzled by this discussion. The distinction in meaning between the words "pretty" and "beautiful" is perfectly clear, even if people might disagree which was the better word to use in one or another specific case. Every other language of which I have any knowledge has two corresponding words. Where's the problem?