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This classifier uses fasttext to detect if an unintended language is used. You can combine this tool together with RulePolicy rules to handle out of scope responses more elegantly. Assuming that you're making an assistant to handle English then you can send the user an appropriate response if this model predicts another language.

The tool should be able to detect 176 languages but the predictions won't be perfect. Especially when the user sends short utterances we need to be careful. That is why this tool allows you to specify a minimum number of characters and tokens before this model triggers an intent.


In order to use this tool you'll need to ensure the correct dependencies are installed.

pip install "rasa_nlu_examples[fasttext] @"

Understanding the Tool

You're encouraged to play with the tool from a jupyter notebook so you can understand what kinds of mistakes the model might make. To do that you'll first want to download the fasttext library as well as the pretrained model.

python -m pip install fasttext

Then from a notebook you should be able to interact with the model by running:

import fasttext
model = fasttext.load_model("lid.176.ftz")

txt = "i am speaking english"
proba_dict = {k: v for k, v in zip(*model.predict(txt, k=10))}

Configurable Variables

  • expected_language (required): the language that you expect to be predicted. If this language is predicted we won't trigger an intent.
  • intent_triggered (required): the name of the intent to trigger when the model does not detect the expected language.
  • cache_dir (required): specifies the folder where the pretrained model can be found.
  • model_file (required): specifies the path to a pretrained model file, typically you'll want lid.176.ftz. See the fasttext docs for more info.
  • threshold (default: 0.7): if the probability for your language is smaller than this threshold then we trigger the intent.
  • min_tokens (default: 3): the minimum number of tokens that need to be in the utterance. If there's less tokens the language model is ignored because it is likely to be in-accurate.
  • min_chars (default: 10): the minimum number of characters of text that need to be in the utterance. If there's less tokens the language model is ignored because it is likely to be in-accurate.
  • protected_intents (default: []): specifies a list of intent names that won't be overwritten

Base Usage

The configuration file below demonstrates how you might use the this component. In this example we've assumed that you've downloaded the lightweight "lid.176.ftz" model beforehand and that it exists in the downloaded folder that is on the root path of your project.

language: en

- name: WhitespaceTokenizer
- name: LexicalSyntacticFeaturizer
- name: CountVectorsFeaturizer
  analyzer: char_wb
  min_ngram: 1
  max_ngram: 4
- name: DIETClassifier
  epochs: 1
- name: rasa_nlu_examples.fallback.FasttextLanguageFallbackClassifier
  expected_language: en
  intent_triggered: non_english
  cache_dir: downloaded
  file: 'lid.176.ftz'
  min_chars: 5
  min_tokens: 2
  threshold: 0.3
  protected_intents: ["greet"]

To get the most out of this tool you also need to add a rule to a rules.yml file. That way you can configure an appropriate action whenever a user is speaking in the wrong language. That might look something like this:


- rule: Ask the user to switch to speaking in English.
  - intent: non_english
  - action: utter_non_english

For more information on rules, see the docs.