added-bart-japanese-tokenizer
Author: p-s-p-s
Pull request: yes

# What does this PR do?

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This PR adds support for pre-trained BART models for Japanese text.
The original pre-trained model was converted from the Fairseq checkpoint which contains an extra layer_norm layer after the encoder and decoder, therefore compatible with the MBart model. Details of the model can be found [here](https://huggingface.co/Formzu/bart-large-japanese).

Since Japanese language tokenization requires text segmentation, half-width character conversion, as well as special token compatibility with the existing checkpoint, a new tokenizer was implemented.

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Models:

- albert, bert, xlm: @LysandreJik
- blenderbot, bart, marian, pegasus, encoderdecoder,  t5: @patrickvonplaten, @patil-suraj
- longformer, reformer, transfoxl, xlnet: @patrickvonplaten
- fsmt: @stas00
- funnel: @sgugger
- gpt2: @patrickvonplaten, @LysandreJik
- rag: @patrickvonplaten, @lhoestq
- tensorflow: @LysandreJik

Library:

- benchmarks: @patrickvonplaten
- deepspeed: @stas00
- ray/raytune: @richardliaw, @amogkam
- text generation: @patrickvonplaten
- tokenizers: @n1t0, @LysandreJik
- trainer: @sgugger
- pipelines: @LysandreJik

Documentation: @sgugger

HF projects:

- datasets: [different repo](https://github.com/huggingface/datasets)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Examples:

- maintained examples (not research project or legacy): @sgugger, @patil-suraj
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Comments:
_The documentation is not available anymore as the PR was closed or merged._

Thanks a lot for your PR. This custom tokenizer should really go on the Hub in the repos that use it, using our [code on the Hub](https://huggingface.co/docs/transformers/custom_models) feature, instead of adding a new model though.

@sgugger Thanks for the advice. I added custom tokenizer code as well as AutoTokenizer support to the model on the Hub.