Title: Cannot download wmt16 dataset
Author: vidyasiv
State: closed

### Describe the bug

As of this morning (PST) 2/1/2024, seeing the wmt16 dataset is missing from opus , could you suggest an alternative?

```
Downloading data files:   0%|                                                                                                                     | 0/4 [00:00<?, ?it/s]Traceback (most recent call last):
  File "test.py", line 2, in <module>
    raw_datasets = load_dataset("wmt16","ro-en",split="train")
  File "/usr/local/lib/python3.8/dist-packages/datasets/load.py", line 2153, in load_dataset
    builder_instance.download_and_prepare(
  File "/usr/local/lib/python3.8/dist-packages/datasets/builder.py", line 954, in download_and_prepare
    self._download_and_prepare(
  File "/usr/local/lib/python3.8/dist-packages/datasets/builder.py", line 1717, in _download_and_prepare
    super()._download_and_prepare(
  File "/usr/local/lib/python3.8/dist-packages/datasets/builder.py", line 1027, in _download_and_prepare
    split_generators = self._split_generators(dl_manager, **split_generators_kwargs)
  File "/root/.cache/huggingface/modules/datasets_modules/datasets/wmt16/746749a11d25c02058042da7502d973ff410e73457f3d305fc1177dc0e8c4227/wmt_utils.py", line 754, in _split_generators
    downloaded_files = dl_manager.download_and_extract(urls_to_download)
  File "/usr/local/lib/python3.8/dist-packages/datasets/download/download_manager.py", line 565, in download_and_extract
    return self.extract(self.download(url_or_urls))
  File "/usr/local/lib/python3.8/dist-packages/datasets/download/download_manager.py", line 428, in download
    downloaded_path_or_paths = map_nested(
  File "/usr/local/lib/python3.8/dist-packages/datasets/utils/py_utils.py", line 464, in map_nested
    mapped = [
  File "/usr/local/lib/python3.8/dist-packages/datasets/utils/py_utils.py", line 465, in <listcomp>
    _single_map_nested((function, obj, types, None, True, None))
  File "/usr/local/lib/python3.8/dist-packages/datasets/utils/py_utils.py", line 384, in _single_map_nested
    mapped = [_single_map_nested((function, v, types, None, True, None)) for v in pbar]
  File "/usr/local/lib/python3.8/dist-packages/datasets/utils/py_utils.py", line 384, in <listcomp>
    mapped = [_single_map_nested((function, v, types, None, True, None)) for v in pbar]
  File "/usr/local/lib/python3.8/dist-packages/datasets/utils/py_utils.py", line 367, in _single_map_nested
    return function(data_struct)
  File "/usr/local/lib/python3.8/dist-packages/datasets/download/download_manager.py", line 454, in _download
    return cached_path(url_or_filename, download_config=download_config)
  File "/usr/local/lib/python3.8/dist-packages/datasets/utils/file_utils.py", line 182, in cached_path
    output_path = get_from_cache(
  File "/usr/local/lib/python3.8/dist-packages/datasets/utils/file_utils.py", line 596, in get_from_cache
    raise FileNotFoundError(f"Couldn't find file at {url}")
FileNotFoundError: Couldn't find file at https://opus.nlpl.eu/download.php?f=SETIMES/v2/tmx/en-ro.tmx.gz
```


### Steps to reproduce the bug

```
from datasets import load_dataset
raw_datasets = load_dataset("wmt16","ro-en",split="train")
```

### Expected behavior

Expect the dataset to be downloaded/ at least a clean exit with error explaining dataset is missing and a suggestion for next steps

### Environment info

- `datasets` version: 2.14.7
- Platform: Linux-5.15.0-92-generic-x86_64-with-glibc2.29
- Python version: 3.8.10
- Huggingface_hub version: 0.17.3
- PyArrow version: 15.0.0
- Pandas version: 2.0.1