When people speak Hebrew, they say Hashem instead of Y-HVH, because saying His name is impossible/forbidden. Additionally, when writing, some people write G-d instead of God. Why when speaking English aren't people careful to say Gosh?
Many people are careful not to say a translation of one of G-d's 7 holy names (see here for the Rambam's version of them).
G-d is a translation of either A-D-N-Y or Y-H-V-H, depending on who you ask.
This is why many people use the word Hashem ("The Name") in Hebrew, or Aibishter ("One Above") in Yiddish.
See this article, which says that R' Moshe Feinstein held that if one made a blessing using the Yiddish word G-t instead of the Hebrew name of G-d, he fulfilled his obligation, and posits that R' Moshe would say the same thing if the English G-d was used.
There should be more direct sources that speak about saying a translation of G-d's names, but I can't find them right now.
The Shach (Yoreh De'ah 179:11) ruled that "God" spelled in a foreign language does NOT have the status of a "shem" and thus may be erased, lehatkhila. For more information, you can read this article: http://www.shamash.org/lists/scj-faq/HTML/faq/11-03-01.html