i have heard that japanes don not use english much but in bing ads you do not have japanes optionskeywords will be in english but keep your ad in japanese so more people will be attracted towards your ad and you get more traffic.
i guess you are absolutly rightI really hope you know what you are doing. South Asian countries don't really prefer English so much. 90% of them will opt for the ads which are in their native languages. In your case, its Japan so I wouldn't bet so much