Setup

I am reporting a problem with Biopython version, Python version, and operating
system as follows:

>>> import sys; print(sys.version)
3.8.17 | packaged by conda-forge | (default, Jun 16 2023, 07:11:34) 
[Clang 14.0.6 ]
>>> import platform; print(platform.python_implementation()); print (platform.platform())
CPython
macOS-10.16-x86_64-i386-64bit
>>> import Bio
>>> print(Bio.__version__)
1.81

(Please copy and run the above in your Python, and copy-and-paste the output)

Expected behaviour

In the PDB header there is a deposition date in xx-xxx-xx format. If this is filled out with non-english month month abbreviations (e.g. Okt for October or Ago for August), Biopython should assign the month to be '0' as it does for the xxx case

Actual behaviour

Reproduced from parse_pdb_header._format_date function:

In [3]: pdb_date = "21-Ago-23"

In [4]: month = str(all_months.index(pdb_date[3:6]))
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[4], line 1
----> 1 month = str(all_months.index(pdb_date[3:6]))

ValueError: 'Ago' is not in list

Proposed solution:

We should make a check in the _format_date function that the string being checked is actually in the all_months list and if not set the month to '0'.