Update languages in aeslc dataset card (#3357)

Update README.md

After having worked a bit with the dataset.
As far as I know, it is solely in English (en-US). There are only a few mails in Spanish, French or German (less than a dozen I would estimate)

Commit from https://github.com/huggingface/datasets/commit/365773b3eec3da978fff62772e2169ea958460c3

README.md

@@ -74,7 +74,7 @@ There are two features:
 
 ### Languages
 
-[More Information Needed](https://github.com/huggingface/datasets/blob/master/CONTRIBUTING.md#how-to-contribute-to-the-dataset-cards)
+Monolingual English (mainly en-US) with some exceptions.
 
 ## Dataset Structure