Discovering Unusual Word Usages with Masked Language Model via Pseudo-label Training

User-generated texts contain not only non-standard words such as b4 for before, but unusual word usages such as catfish for a person who uses fake identity online, which requires knowledge about the words to handle such cases in natural language processing. We present a neural model for detecting the non-standard usages in social media text. To deal with the lack of training data for this task, we propose a method for synthetically generating pseudo non-standard examples from a corpus, which enables us to train the model without manually-annotated training data and for any arbitrary language. Experimental results on Twitter and Reddit datasets show that our proposed method achieves better performance than existing methods, and is effective across different languages.