User blog comment:Akrie/May 7th Events & Updates~!/@comment-25889587-20150508173709/@comment-25968376-20150510155752

Well there is a /en/ page, which is what we get in Indonesian, even from the in-game message link. It's most likely a server misconfiguration.

Line is Japanese and most of their users are from Taiwan and Thailand, so it makes sense for them to focus on East Asia and their languages, but they could afford to hire some bug testers and proper translators :P