From the official documentation, it looks like you can only use Python API to access Featurestore.

And only Python API reference is available on the Documentation page.

You need a featurestoreclient(Only available to python) to write the table to featurestore.

1. What languages can be utilized to write data frames as feature tables in the Feature Store? Python
2. Can models in R, SparkR, or Scala used for inference, access the Feature Store ? No

However, if you understand the underlying storage of FeatureStore, it's just a delta table. You can use any other DataframeAPI available in Scala, Java, Python and R and write to the delta table.

And the register the existing Delta Table as a feature table using python API.

Reference:

Register an existing Delta table as a feature table

https://learn.microsoft.com/en-us/azure/databricks/machine-learning/feature-store/feature-tables#cre...

A feature table is stored as a Delta table. 

https://learn.microsoft.com/en-us/azure/databricks/machine-learning/feature-store/troubleshooting-an...