Flair is:

A powerful NLP library. Flair allows you to apply our state-of-the-art natural language processing (NLP) models to your text, such as named entity recognition (NER), part-of-speech tagging (PoS), sense disambiguation and classification, with support for a rapidly growing number of languages.

It is multilingual and allows you to use and combine different word and document embeddings, including the BERT embeddings, ELMo embeddings, and their proposed Flair embeddings. In addition, Flair allows you to train your own language model, targeted to your language or domain, and apply it to the downstream task.