Regarding the use of ISO language standards on in @lang_from @lang_to:
1) I believe these should be lower case according to ISO 639-3
2) It might make sense to add all languages, the space needed is negligible. If making a selection perhaps focus on the largest ones: e.g. Chinese "zho" is not in the DTD, but the much rarer "zha" Chuang/Zhuang is.
Regarding the use of ISO language standards on in @lang_from @lang_to:
1) I believe these should be lower case according to ISO 639-3
2) It might make sense to add all languages, the space needed is negligible. If making a selection perhaps focus on the largest ones: e.g. Chinese "zho" is not in the DTD, but the much rarer "zha" Chuang/Zhuang is.