FROM Halachically Speaking-Kof-K
Horav Chaim Pinchus Sheinberg Shlita is of the opinion that a person who went through the mesechta with an English translation may make a siyum. However, the person who is using the English has to be actually working on understanding the Gemorah and not just reading the words like a book. For a person who needs the English, working through the entire Gemorah in English, is a very big simcha.