add english language tags for ~100 datasets
Fixing the tags of all the datasets is out of scope for this PR so I'm merging even though the CI fails because of the missing tags
As discussed on Slack, I have manually checked for ~100 datasets that they have at least one subset in English. This information was missing so adding into the READMEs.

Note that I didn't check all the subsets so it's possible that some of the datasets have subsets in other languages than English...