What I am thinking as an English native speaking to you
If I genuinely don't understand I will say it gently. I also tend to use more specific language what do you mean? This makes it clear to the listeners why I don't understand. It is not always about bad grammar or misusing a word
I won't correct every little thing to keep the flow of the conversation going and not overload you with information only if I feel it will impede understanding unless it is practice situation and you want me to. I learned that the hard way in a college class. The person felt like I was distracting her. Accuracy comes with time. The courage to express yourself is priceless.
Yes I realize that communicating with second language speakers is an art that few natives possess unless they have studied a foreign language themselves. Simplification is hard because it hard to assess the learner's level unless they are obviously bad. I have a Peruvian friend who speaks really well but occasionally I will confuse him with what I say That's why many learners feel imitated by trying to speak to a group of natives who are not used to second language speakers. There the pressure to express yourself just right and they will throw around colloquialism and other informal language that you don't understand. This also why it hard for me to admit I don't understand and is why when I am speaking with a group of Spanish natives I freely admit that I speak it only as second language.
Your pronunciation doesn't have to be perfect as long as it is understandable. I will admit that English pronunciation can be complex and depending on your native language there are many sounds that are completely new and the spelling doesn't give you clues. Although adults can learn languages as well if not better to than children children have an advantage in phonetics. Their brains have not formed around the sounds of their native language yet making it easier for them to pick up on new ones. As adults, it harder to pick up on completely new sounds or reproduce them welle . I have this problem with Brazilian Portuguese. I can hardly tell the difference between the open and closed vowel sounds. Spanish speakers tend to soften the fricative s in English as in boys and disease and the il sound . This is why I believe accent reduction and not accent elimination .