[model site] missing language tags for t5 models
Would it be possible to update core t5-* models' cards to include what languages they were trained on? Currently it says "en", which is very lacking.

e.g., see: 
* https://huggingface.co/t5-base
* https://huggingface.co/t5-small
* etc.

The core t5 models should somehow have hits with https://huggingface.co/models?search=t5&filter=de, but they don't. Probably because they aren't tagged with the language tags. So they aren't found.

From: https://s3.amazonaws.com/models.huggingface.co/bert/t5-small-config.json
it looks like: French/German/Romanian. But also it looks to only support one direction, so probably adding the following would be clear enough to the end user:

* en_to_fr
* en_to_ge
* en_to_ro

Thank you.

@patrickvonplaten

I updated all 5 models to include fr/ro/de language tags.