Thank you. I begin to see that, as I progress, everything is gradually explained. But sometimes one just wants for his voice to be heard. Many words are identical or quite similar in serbian language (of course), and I enjoy tracking those. Thank's again, you are doing a great job!
Without any doubt :) Vidu ankaŭ https://eo.wikipedia.org/wiki/Pola_lingvo#Polaj_vortoj_en_Esperanto
English "this", in Nominative (the basic case, used e.g. for the subject of the sentence) can have three forms: "ten" (masculine), "ta" (feminine), "to" (neuter) - dependent on the gender of the noun they describe.
"chłopiec" (a boy) is obviously masculine, so "ten chłopiec".
"this bad" would be a different situation, as it means more or less "so bad". "Czy ten chłopiec jest tak zły/tak bardzo zły?"