File > Download option defaults to .py for non-Python runtimes (R, Julia)

[ayyucedemirbas]

Describe the current behavior
When using a notebook configured with a non-Python runtime (R or Julia), the File > Download menu options do not adapt to the active kernel.

The menu continues to show "Download .py" as the only script export option. When selected, the file is downloaded with a .py extension. This requires the user to manually rename the file extension locally (e.g., from script.py to script.R) to use it properly in other IDEs.

Describe the expected behavior
The download menu should be context-aware based on the active Runtime type.

• If the Runtime is R, the menu should display "Download .R" and save the file with a .R extension.
• If the Runtime is Julia, the menu should display "Download .jl" and save the file with a .jl extension.

What web browser you are using
Chrome Version 143.0.7499.170 (Official Build) (arm64)

Additional context
Steps to reproduce the behavior:

1. Open a new Google Colab notebook: https://colab.research.google.com/drive/1MwEd8VDmQ2ma7eO4mqeazMvdgk7Dz_-l?usp=sharing
2. Go to Runtime > Change runtime type.
3. Select R (or utilize a Julia kernel).
4. Enter valid R code into a cell (e.g., print("Hello R")).
5. Navigate to File > Download.
6. Observe that the option remains "Download .py" and results in a Python file download.

[metrizable]

@ayyucedemirbas Thanks for using Colab and filing the feature request. Tracking internally at b/476204068.