Migrate model card from transformers-repo

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Original file history: https://github.com/huggingface/transformers/commits/master/model_cards/bert-base-multilingual-cased-README.md

README.md

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+---
+language: multilingual
+license: apache-2.0
+datasets:
+- wikipedia
+---
+
+# BERT multilingual base model (cased)
+
+Pretrained model on the top 104 languages with the largest Wikipedia using a masked language modeling (MLM) objective.
+It was introduced in [this paper](https://arxiv.org/abs/1810.04805) and first released in
+[this repository](https://github.com/google-research/bert). This model is case sensitive: it makes a difference
+between english and English.
+
+Disclaimer: The team releasing BERT did not write a model card for this model so this model card has been written by
+the Hugging Face team.
+
+## Model description
+
+BERT is a transformers model pretrained on a large corpus of multilingual data in a self-supervised fashion. This means
+it was pretrained on the raw texts only, with no humans labelling them in any way (which is why it can use lots of
+publicly available data) with an automatic process to generate inputs and labels from those texts. More precisely, it
+was pretrained with two objectives:
+
+- Masked language modeling (MLM): taking a sentence, the model randomly masks 15% of the words in the input then run
+  the entire masked sentence through the model and has to predict the masked words. This is different from traditional
+  recurrent neural networks (RNNs) that usually see the words one after the other, or from autoregressive models like
+  GPT which internally mask the future tokens. It allows the model to learn a bidirectional representation of the
+  sentence.
+- Next sentence prediction (NSP): the models concatenates two masked sentences as inputs during pretraining. Sometimes
+  they correspond to sentences that were next to each other in the original text, sometimes not. The model then has to
+  predict if the two sentences were following each other or not.
+
+This way, the model learns an inner representation of the languages in the training set that can then be used to
+extract features useful for downstream tasks: if you have a dataset of labeled sentences for instance, you can train a
+standard classifier using the features produced by the BERT model as inputs.
+
+## Intended uses & limitations
+
+You can use the raw model for either masked language modeling or next sentence prediction, but it's mostly intended to
+be fine-tuned on a downstream task. See the [model hub](https://huggingface.co/models?filter=bert) to look for
+fine-tuned versions on a task that interests you.
+
+Note that this model is primarily aimed at being fine-tuned on tasks that use the whole sentence (potentially masked)
+to make decisions, such as sequence classification, token classification or question answering. For tasks such as text
+generation you should look at model like GPT2.
+
+### How to use
+
+You can use this model directly with a pipeline for masked language modeling:
+
+```python
+>>> from transformers import pipeline
+>>> unmasker = pipeline('fill-mask', model='bert-base-multilingual-cased')
+>>> unmasker("Hello I'm a [MASK] model.")
+
+[{'sequence': "[CLS] Hello I'm a model model. [SEP]",
+  'score': 0.10182085633277893,
+  'token': 13192,
+  'token_str': 'model'},
+ {'sequence': "[CLS] Hello I'm a world model. [SEP]",
+  'score': 0.052126359194517136,
+  'token': 11356,
+  'token_str': 'world'},
+ {'sequence': "[CLS] Hello I'm a data model. [SEP]",
+  'score': 0.048930276185274124,
+  'token': 11165,
+  'token_str': 'data'},
+ {'sequence': "[CLS] Hello I'm a flight model. [SEP]",
+  'score': 0.02036019042134285,
+  'token': 23578,
+  'token_str': 'flight'},
+ {'sequence': "[CLS] Hello I'm a business model. [SEP]",
+  'score': 0.020079681649804115,
+  'token': 14155,
+  'token_str': 'business'}]
+```
+
+Here is how to use this model to get the features of a given text in PyTorch:
+
+```python
+from transformers import BertTokenizer, BertModel
+tokenizer = BertTokenizer.from_pretrained('bert-base-multilingual-cased')
+model = BertModel.from_pretrained("bert-base-multilingual-cased")
+text = "Replace me by any text you'd like."
+encoded_input = tokenizer(text, return_tensors='pt')
+output = model(**encoded_input)
+```
+
+and in TensorFlow:
+
+```python
+from transformers import BertTokenizer, TFBertModel
+tokenizer = BertTokenizer.from_pretrained('bert-base-multilingual-cased')
+model = TFBertModel.from_pretrained("bert-base-multilingual-cased")
+text = "Replace me by any text you'd like."
+encoded_input = tokenizer(text, return_tensors='tf')
+output = model(encoded_input)
+```
+
+## Training data
+
+The BERT model was pretrained on the 104 languages with the largest Wikipedias. You can find the complete list
+[here](https://github.com/google-research/bert/blob/master/multilingual.md#list-of-languages).
+
+## Training procedure
+
+### Preprocessing
+
+The texts are lowercased and tokenized using WordPiece and a shared vocabulary size of 110,000. The languages with a
+larger Wikipedia are under-sampled and the ones with lower resources are oversampled. For languages like Chinese,
+Japanese Kanji and Korean Hanja that don't have space, a CJK Unicode block is added around every character. 
+
+The inputs of the model are then of the form:
+
+```
+[CLS] Sentence A [SEP] Sentence B [SEP]
+```
+
+With probability 0.5, sentence A and sentence B correspond to two consecutive sentences in the original corpus and in
+the other cases, it's another random sentence in the corpus. Note that what is considered a sentence here is a
+consecutive span of text usually longer than a single sentence. The only constrain is that the result with the two
+"sentences" has a combined length of less than 512 tokens.
+
+The details of the masking procedure for each sentence are the following:
+- 15% of the tokens are masked.
+- In 80% of the cases, the masked tokens are replaced by `[MASK]`.
+- In 10% of the cases, the masked tokens are replaced by a random token (different) from the one they replace.
+- In the 10% remaining cases, the masked tokens are left as is.
+
+
+### BibTeX entry and citation info
+
+```bibtex
+@article{DBLP:journals/corr/abs-1810-04805,
+  author    = {Jacob Devlin and
+               Ming{-}Wei Chang and
+               Kenton Lee and
+               Kristina Toutanova},
+  title     = {{BERT:} Pre-training of Deep Bidirectional Transformers for Language
+               Understanding},
+  journal   = {CoRR},
+  volume    = {abs/1810.04805},
+  year      = {2018},
+  url       = {http://arxiv.org/abs/1810.04805},
+  archivePrefix = {arXiv},
+  eprint    = {1810.04805},
+  timestamp = {Tue, 30 Oct 2018 20:39:56 +0100},
+  biburl    = {https://dblp.org/rec/journals/corr/abs-1810-04805.bib},
+  bibsource = {dblp computer science bibliography, https://dblp.org}
+}
+```