

TITLE
run_pl_glue.py (almost equivalent performance with non-english bert models)

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## Environment info
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- `transformers` version: `4.0.0.dev0`
- Platform: `Ubuntu 20.04.1 LTS`
- Python version: `3.8.5`
- PyTorch version (GPU?): `1.7.0` (GPU - yes)
- Tensorflow version (GPU?):
- Using GPU in script?: Yes (GeForce GTX Titan X)
- Using distributed or parallel set-up in script?: distributed

### Who can help
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 albert, bert, GPT2, XLM: @LysandreJik 
 tokenizers: @mfuntowicz
 Trainer: @sgugger
 Speed and Memory Benchmarks: @patrickvonplaten
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 TextGeneration: @TevenLeScao 
 examples/distillation: @VictorSanh
 nlp datasets: [different repo](https://github.com/huggingface/nlp)
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 examples/bert-loses-patience: @JetRunner
 tensorflow: @jplu
 examples/token-classification: @stefan-it
 documentation: @sgugger
 --> perhaps @sgugger

## Information
I tested running the glue benchmark with a few non-english models such as; Arabic, Swedish and Chinese.
Models I am using: `asafaya/bert-base-arabic`, `KB/bert-base-swedish-cased`, `bert-base-chinese`.

I recieve almost identical results as in [Run PyTorch version](https://github.com/huggingface/transformers/tree/master/examples/text-classification#run-pytorch-version), it differs with a few percentages for each task, where some are even slightly better than using the default `bert-base-cased`

Am not sure this is a bug, but it seems a bit strange that with using different embeddings that are really far away from English such as Arabic and Chinese I get very similair results.

The problem arises when using:
* [X] the official example scripts: [run_glue.py](https://github.com/huggingface/transformers/blob/master/examples/text-classification/run_glue.py)
* [ ] my own modified scripts: (give details below)

The tasks I am working on is:
* [X] an official GLUE/SQUaD task: GLUE, (sts-b in this example)
* [ ] my own task or dataset: (give details below)

## To reproduce

I get almost identical results when running a non-english bert on the glue benchmark. In this case on `stsb` using the `bert-base-chinese`, `asafaya/bert-base-arabic` and `KB/bert-base-swedish-cased`.

```
export TASK_NAME=stsb

python run_glue.py \
  --model_name_or_path bert-base-chinese \
  --task_name $TASK_NAME \
  --do_train \
  --do_eval \
  --max_seq_length 128 \
  --per_device_train_batch_size 32 \
  --learning_rate 2e-5 \
  --num_train_epochs 3.0 \
  --output_dir /tmp/$TASK_NAME/
```
Chinese:
```
11/18/2020 17:10:42 - INFO - __main__ -   ***** Eval results stsb *****
11/18/2020 17:10:42 - INFO - __main__ -     eval_loss = 0.8410218954086304
11/18/2020 17:10:42 - INFO - __main__ -     eval_pearson = 0.7922208042884891
11/18/2020 17:10:42 - INFO - __main__ -     eval_spearmanr = 0.7956508384154777
11/18/2020 17:10:42 - INFO - __main__ -     eval_combined_score = 0.7939358213519834
11/18/2020 17:10:42 - INFO - __main__ -     epoch = 3.0
```
Arabic:
```
11/18/2020 17:14:04 - INFO - __main__ -   ***** Eval results stsb *****
11/18/2020 17:14:04 - INFO - __main__ -     eval_loss = 0.8082903027534485
11/18/2020 17:14:04 - INFO - __main__ -     eval_pearson = 0.8357733212850804
11/18/2020 17:14:04 - INFO - __main__ -     eval_spearmanr = 0.8386964712863125
11/18/2020 17:14:04 - INFO - __main__ -     eval_combined_score = 0.8372348962856965
11/18/2020 17:14:04 - INFO - __main__ -     epoch = 3.0
```
Swedish:
```
11/18/2020 17:32:26 - INFO - __main__ -   ***** Eval results stsb *****
11/18/2020 17:32:26 - INFO - __main__ -     eval_loss = 0.7071832418441772
11/18/2020 17:32:26 - INFO - __main__ -     eval_pearson = 0.8379047445076137
11/18/2020 17:32:26 - INFO - __main__ -     eval_spearmanr = 0.8350383734219187
11/18/2020 17:32:26 - INFO - __main__ -     eval_combined_score = 0.8364715589647662
11/18/2020 17:32:26 - INFO - __main__ -     epoch = 3.0
```
Is expected behaviour? Meaning that the readaption of the embedding matrices can work with non english vocabs such as Chinese and Arabic since they perhaps contain some latin characters. 

With English model `bert-base-cased` we get pearson: `83.95` and Arabic model `asafaya/bert-base-arabic` pearson: `83.57`. 
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Thanks!
## Expected behavior
Not sure..
<!-- A clear and concise description of what you would expect to happen. -->
