English is one of the easiest languages to become "understandable" in. Presumably because of how many people invaded England historically. When another culture invades, some of the language rules are adopted, but they are universally the simpler rules, and the more advanced rules aren't integrated.

Spoken English, with it's reliance on word order, lack of genders, relative lack of verb conjugations and noun declensions make it ridiculously easy to be understood in comparison to other languages. You won't be Shakespeare, but you will be able to communicate.

Written English, admittedly, is much harder (mostly because of the early standardization), but enough natives also have trouble spelling enough words that you can still be understood.