You realize the name of the expansion in Japanese is ALSO Heavensward, right?
http://jp.finalfantasyxiv.com/heavensward/
It is extremely common for Japanese companies to produce material and name it in English, then use a subtitle to back-translate it into Japanese for the Japanese audience. Source: I have a degree in Japanology :|
The official name of the expansion in Japanese is
Heavensward: Final Fantasy XIV Online
蒼天のイシュガルド ファイナルファンタジーXIV
You can see it in the banner at the bottom of the page
http://jp.finalfantasyxiv.com/pr/ . Notice how the Japanese text is significantly smaller and off to the side. It's there as a subtitle, the NAME of the game is Final Fantasy XIV Online, NOT ファイナルファンタジーXIV, and the expansion is named Heavensward, NOT 蒼天のイシュガルド. If you take issue with the Japanese using English names as official names for products, you can take that up with the entire country of Japan and its culture?