There is power in sound. So certain words that vibrate a special way or contain specific sound are power words. But just writing a spell in another language or speaking a spell in another language will not make it more powerful.
If you want to learn more about the power in language and sound, I suggest reading "Magic, Power, Language, Symbol" by Patrick Dunn. It is the easiest to read and most informative book on the subject I have read to date and I feel it has even helped me to gain a greater understanding of what I've already been practicing. Now instead of just practicing it "because it works" I understand WHY it works, which gives me a firmer belief on its effectiveness. Since it is an overview, it will lead you into deeper research of the specific subjects you find most interesting.