Ensure proper formatting of the code block

[robertjank]

This is a follow-up issue for issue #13 Ensure proper formatting of the title tag. See also issue #80 Ensure proper formatting of the legend tag.

Similar to the collapse blocks that contain a title tag, the code blocks contain a language tag:
--- code ---
---
language: python
---

Optionally, there are some additional tags:
--- code ---
---
language: python
filename: main.py
line_numbers: true
line_number_start: 11
line_highlights: 12
---

Everything within the block following the --- code --- line needs to stay in English. So not only the keywords (language, filename, etc.) should be corrected when necessary, but also the values (python, main.py, etc.).