Add `language_bcp47` tag (#4753)

* fix ms_terms

* fix ted_talks_iwslt

* move tags to language_bcp47

* fix bad codes

* add language_details and language_bcp47 in DatasetMetadata

* more fixes

* fix wiki_dpr

Commit from https://github.com/huggingface/datasets/commit/aa48a29d1304167dff37cef0ed7542f29376ee2d

README.md

@@ -7,6 +7,8 @@ language_creators:
 - crowdsourced
 - expert-generated
 language:
+- ru
+language_bcp47:
 - ru-RU
 license:
 - mit