text: 
  
  TITLE
  `offset_mapping` is strange for non-ascii token
  
  COMMENTS
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  BODY
  ### System Info
  
  ```shell
  - Tensorflow version (GPU?): not installed (NA)
  - Flax version (CPU?/GPU?/TPU?): not installed (NA)
  - Jax version: not installed
  - JaxLib version: not installed
  - Using GPU in script?: <fill in>
  ```
  
  
  ### Who can help?
  
  @SaulLu
  
  ### Information
  
  - [ ] The official example scripts
  - [X] My own modified scripts
  
  ### Tasks
  
  - [ ] An officially supported task in the `examples` folder (such as GLUE/SQuAD, ...)
  - [X] My own task or dataset (give details below)
  
  ### Reproduction
  
  1. Use BertTokenizerFast
  2. tokenize the text 
  text = "The Dungan Revolt ( 1862–77 ) or Tongzhi Hui Revolt ( , Xiao'erjing : توْحُوِ بِيًا/لُوًا ,  ) or Hui ( Muslim ) Minorities War was a mainly ethnic and religious war fought in 19th-century western China , mostly during the reign of the Tongzhi Emperor ( r. 1861–75 ) of the Qing dynasty ."
  outputs = self.tokenizer(text,
                                      padding="max_length",
                                      truncation=False,
                                      max_length=self.config.max_seq_length,
                                      return_offsets_mapping=True)
  3. The `offset_mapping` missed some subtokens, for example, the subtoken at the char position 79. 
  
  <img width="83" alt="截屏2022-04-20 下午8 46 55" src="https://user-images.githubusercontent.com/39556019/164233684-192d1c32-0f67-4198-8e59-e60426fce32d.png">
  
  
  ### Expected behavior
  
  ```shell
  the offset_mapping should be:
  [... 
   (70, 71),
   (71, 72),
   (73, 74),
   (76, 77),
   (78, 80), # this line ****
   (81, 82),
   (83, 84),
  ... ]
  ```
  