The English language
The most widely spoken, the most influential, and the lingua franca of choice (the common language used between speakers whose native languages are different).
It is also notoriously difficult to learn. As a native speaker, and being fluent in both Italian and Mandarin Chinese, I am amazed at how so many people manage to speak English as well as they do. I also understand why so many struggle to learn this crazy language that I love.
Multiple meanings for the same word is just one of the difficulties. Take the word fix. It can mean so many things and be used in so many ways. Here are just a few:
Fix: To mend or repair.
Ex: "I have a flat tire which I need to get fixed."
Fix: to get ready, prepare.
Ex: "I'm fixing to fix breakfast."
Translation: I'm about to prepare breakfast.
Fix: To castrate or spay (neuter) an animal, usually a pet.
Ex: "I get all of my pets fixed."
Fix: To satisfy an addiction. A thing or activity that gives a person a feeling of euphoria or pleasure that is difficult to do without.
Ex: "Sometimes I really need an In-n-Out burger fix."
Fix: A predicament (a difficult or awkward situation).
Ex: "How on earth did you get into such a fix?"
Fix: To set up. To arrange a date for.
Ex: "I want to fix you up with my cousin. You'll really like her."
Fix: Restore order or tidiness to.
Ex: "He really needs to fix his hair."
Fix: To influence the outcome by illegal or unethical means.
Ex: "There is no doubt that the election was fixed."
Fix or Fixie: A single speed fixed wheel bicycle.
Ex: "My favorite bikes are fixies."
The above definition is of course my favorite. On a beautiful day I love to get my exercise fix by jumping on my fixie and hitting the road. There's nothing better.