Of course we did have our own brand of fun with it. If you check carefully, the regular rules do not prohibit foreign (non-English) words. So my usual partner and I made some house rules. Between the two of us, we spoke English, some German (him), French (me), and I had Swedish and Latin dictionaries, as well as a couple of short guides to Klingon and Vulcan. I think we also allowed Romulan, though I had no guides for that. I did have my novels handy, though, and one time I went to the bookshelf, pulled out my copy of The Romulan Way by Diane Duane, pointed to the word, and said, "See, it's a word."
The rule was that foreign words were legal if the person using them could point to them in a dictionary/language guide. I briefly regretted that rule one night, when he showed up with the Oxford English Dictionary (three VERY LARGE volumes that wouldn't even fit on the kitchen table along with the game board and our snacks.
We also, just for the fun of it, had a rule that each person, once in a game, could use a "nonsense word" - a word that sounded like an ordinary English word, and was subject to being vetoed by the other player. It couldn't be used to get the 50-point bonus, even if it used 7 tiles. We usually didn't rely on this, just using it when either truly stumped or if an opportunity came to use a word with a funny misspelling.
Oh, and the rules for the Klingon and Vulcan words followed the ordinary rules - no proper nouns or anything normally capitalized. So if a Klingon word had a capital letter in it, it was prohibited (no matter what the word's meaning was).
And I will say that it came in very handy to have memorized the entire Greek alphabet (did that many years ago when I started reading astronomy books and star maps). Greek letters are legal, according to the rules.