Your English probably isn’t terrible. If you understand me, then your English is clearly very good! One small but common mistake though is using the word ‘vocabulary’ instead of ‘dictionary’.
A vocabulary is a stock of known words. It can exist in your head – so for example, we could say ‘My friend has a great vocabulary’ meaning they know a lot of words. Or it can exist in a book (or webpage), and we call this a dictionary. A dictionary contains lots of vocabulary.
Here’s a conversation between two students:
A: My English vocabulary is terrible!
B: I’ll buy you a dictionary for your birthday.
A: Thanks but it’s ok. I prefer to use online dictionaries like Seznam and Google.