Fine-tuning
The paper recommends that the embedding layer and the language adapters are frozen during fine-tuning. A method for doing this is provided:
thon
model.freeze_embeddings_and_language_adapters()
Fine-tune the model 

Cross-lingual transfer
After fine-tuning, zero-shot cross-lingual transfer can be tested by activating the language adapter of the target language:
thon
model.set_default_language("de_DE")
Evaluate the model on German examples 

Resources