It said 'Unable to find file!' What should you do?

ちょっと先日、外国語版のスフィリアについて問い合わせがあったので書いておきますね。

If you tried to start the game and it said 'Unable to find file: Audio/BGM/運命のワルツ', check whether there is Audio/BGM/運命のワルツ.mp3.
Probably not there.

In this case, you have to install a Japanese language pack and set the System Locale to Japanese. Check the following page about details.
https://www.dlsite.com/ecchi-eng/faq/detail/=/type/user/mid/7/did/296

Afterwards, decompress the game in the zip AGAIN.