This old chestnut. I had a quick search through the archives and couldn't find a conclusive answer on this: I'm getting back "cn" for the "iso_639_1" of a spoken language for a movie: http://api.themoviedb.org/3/movie/1422

Now, "cn" is definitely not on the ISO list, but I understand there is some awkwardness around how the various Chinese dialects are represented (technically it should be zh-HK, ie a language-country pair?)

Apologies if this has been asked before, just wondering if it's an content issue (non-ISO 639-1 values shouldn't be allowed for a ISO 639-1 field?) or something we have to live with for now.

Thanks, David