One thing I've found particularly for German speakers is the use of phrases like "since 2 years". A native speaker would say "since 2 years ago", fixing the reference to a definite point in time rather than a duration alone.
My wife is Italian, and it's amazing how many constructs you come across that are correct, but sound odd. Defining rules for many of them in English is almost impossible given the unstructured nature of the language, which drives her mad given her background as a Mathematician.
It also annoys her no end that most people don't correct/question her if they understand the intent of what she said. They feel they'd come across as rude pedants, but she wants to know so that she can improve her grasp of the language.