Sometimes when I am teaching my students ask me why I sometimes say mistake and other times say error. This is what I usually tell them:
Generally speaking, words with hard consonants sound more direct and less diplomatic than those without. So stupid sounds less polite than unwise, unable sounds less harsh than can’t and mistake sounds harder than error. That is one reason.
Another reason is that when I teach English I use the word mistake for when someone does not know something, but error when they do know it but sometimes get it wrong.
So if for example you know the difference between a journey and a trip but sometimes use the wrong one, that is an error. But if you do not know the difference it is a mistake.
The two biggest issues for non native speakers of a language are generalisation and L1 interference. Generalisation is when you learn a language rule and then apply that rule to everything. This is difficult in English because there are so many exceptions to all the rules (irregular verbs are one example). L1 interference is when your first language – your mother tongue – interferes with your other languages. It is like static running through any other languages you learn – particularly ones that are similar to each other, meaning that even if you know the rules of your other languages, you still may have errors popping up because your mother tongue is so deeply embedded. These are more common if you are tired or speak your own language for much of the day. You may suddenly find yourself using the wrong word one out of every four times, or using an Anglicised form of a word in your own language.