Huju, it should be “mistakes in English”. An English mistake is a mistake made by people from England. However, to my great consternation there are very common mistakes in spoken English. Two examples are using “less” to refer to something whose individuals are important (e.g. “less people”) and “there’s” (= there is) when referring to a plural. There is also a certain maggid shiur who constantly uses “a” before a word beginning with a vowel (e.g. “a onion”).
While we are on the subject, I also find it annoying that people constantly say “you know” and use Yiddish words in the middle of English for no apparent reason (e.g. “fregt Rabbi Akiva”). Sometimes it is downright ridiculous. A certain writer wrote about someone finding the Ten Lost Tribes. They wore caftans and streimels and said “Gut Shabbos”.
Anyway, don’t feel bad. Israelis make mistakes in Hebrew. One very common mistake is to use feminine numbers for masculine nouns (e.g. “שלוש עשרה שקל”). They also very often say “כמות של אנשים” instead of “מספר אנשים”. I don’t know who picked it up from whom (not “who” – another common mistake).