Fine-tuning is the second stage in developing a Transfer Learning model. The first stage is pre-training.
In the fine-tuning stage, the model along with its learnings from the pre-training stage is trained on a specific task using a small sample of labelled data. The model’s learnings are ‘fine-tuned’ for the particular task with the labelled data set. After being immersed in a foreign language environment, the fine-tuning stage is like now coming to formally learn the language. Your previous exposure and familiarity with the language will make learning the language a lot easier than if you were just starting from scratch.