🐛 [Dataset] Cannot download wmt14, wmt15 and wmt17
similar slow download speed here for nlp.load_dataset('wmt14', 'fr-en')
`
Downloading: 100%|██████████████████████████████████████████████████████████| 658M/658M [1:00:42<00:00, 181kB/s]
Downloading: 100%|██████████████████████████████████████████████████████████| 918M/918M [1:39:38<00:00, 154kB/s]
Downloading:   2%|▉                                                       | 40.9M/2.37G [04:48<5:03:06, 128kB/s]
`
Could we just download a specific subdataset in 'wmt14', such as 'newstest14'?  > The code runs but the download speed is extremely slow, the same behaviour is not observed on wmt16 and wmt18

The original source for the files may provide slow download speeds.
We can probably host these files ourselves.

> When trying to download wmt17 zh-en, I got the following error:
> ConnectionError: Couldn't reach https://storage.googleapis.com/tfdataset-data/downloadataset/uncorpus/UNv1.0.en-zh.tar.gz

Looks like the file`UNv1.0.en-zh.tar.gz` is missing, or the url changed. We need to fix that

> Could we just download a specific subdataset in 'wmt14', such as 'newstest14'?

Right now I don't think it's possible. Maybe @patrickvonplaten knows more about it
 Yeah, the download speed is sadly always extremely slow :-/. 
I will try to check out the `wmt17 zh-en` bug :-)  Maybe this can be used - https://stuncorpusprod.blob.core.windows.net/corpusfiles/UNv1.0.en-zh.tar.gz.00  These issues seem to be fixed now.
1. I try downloading `wmt14`, `wmt15`, `wmt17`, `wmt19` with the following code:
```
nlp.load_dataset('wmt14','de-en')
nlp.load_dataset('wmt15','de-en')
nlp.load_dataset('wmt17','de-en')
nlp.load_dataset('wmt19','de-en')
```
The code runs but the download speed is **extremely slow**, the same behaviour is not observed on `wmt16` and `wmt18`

2. When trying to download `wmt17 zh-en`, I got the following error:
> ConnectionError: Couldn't reach https://storage.googleapis.com/tfdataset-data/downloadataset/uncorpus/UNv1.0.en-zh.tar.gz