Wrong path for cache directory in offline mode
### Describe the bug

Dear huggingfacers,

I'm trying to use a subset of the-stack dataset. When I run the command the first time

```
dataset = load_dataset(
    path='bigcode/the-stack',
    data_dir='data/fortran',
    split='train' )
```

It downloads the files and caches them normally.

Nevertheless, since my compute nodes are not online (`HF_DATASETS_OFFLINE=1`) . Whenever I try to run the command again, the library is passing the wrong cache path:


`Cache directory for the-stack doesn't exist at /Users/user/.cache/huggingface/datasets/bigcode___the-stack/default-data_dir=data%2Ffortran-data_dir=data%2Ffortran`

when the right path is:

`'/Users/user/.cache/huggingface/datasets/bigcode___the-stack/default-data_dir=data\%2Ffortran`

Not sure why those redundancies are included in the path.  If I try adding the correct path through the the cache_dir argument it throws an error:

ConnectionError: Couldn't reach the Hugging Face Hub for dataset 'bigcode/the-stack': Offline mode is enabled.


Your help with this issue is greatly appreciated. Thanks a lot for the great work.


### Steps to reproduce the bug

1: 

`dataset = load_dataset(
    path='bigcode/the-stack',
    data_dir='data/fortran',
    split='train' )`


2: 

`HF_DATASETS_OFFLINE=1`

3:

`dataset = load_dataset(
    path='bigcode/the-stack',
    data_dir='data/fortran',
    split='train' )`


### Expected behavior

being able to use the cached data

### Environment info

several different systems