Support subword and word language models

Closes #199 (closed)

Ref https://redmine.teklia.com/issues/4941

dan/datasets/extract/extract.py

@@ -365,14 +365,18 @@ class ArkindexExtractor:
                 self.mapping.encode[token]
             ) if token in self.mapping.encode else self.language_tokens.append(token)
         self.language_tokens.append(self.mapping.ctc.encoded)
+        self.language_tokens.append(self.unknown_token)
 
         # Build LM corpus
         train_corpus = [
             text.replace(self.mapping.linebreak.display, self.mapping.space.display)
             for text in self.data["train"].values()
         ]
+
         tokenizer = Tokenizer(
             training_corpus=train_corpus,
+            charset=self.language_tokens,
+            unknown_token=self.unknown_token,
             outdir=self.output / "language_model",
             mapping=self.mapping,
             tokens=self.tokens,