The languages used in displaying anime credits varies from series to series. The second season of Big Windup brought my thoughts on this issue to a head. It is Japanese dub with English sub. The credits during the opening are in Japanese, while the credits in the ending are fully in English. From my experience, this is rare. Subs tend to credit in either the subbed language or Japanese plus other languages.
The latter appears to be the most common choice, at least nowadays. In this case credits tend to be given in the language of the person or company being credited. Japanese nationals will be credited in Japanese, Korean folks in Korean, Filipinos (and other countries using Latin alphabet) in English, etc. I'm not sure about Chinese folks, because I haven't learned to tell the difference between Chinese, and Japanese with a lot of kanji. If a Thai graphics studio worked on the CGI, their credits might well be given in Thai. Anyway, frequently one sees multiple languages on one page of credits.
Is there a style for giving credits that is developing over time, or are they portrayed however the individual studio (or licensee) feels at the time?