Describe the bug
When I create a library with unicode characters (tested with umlauts), the export will not show them properly.

Reproducing

Version: Most current from PyPI

Code:

import bibtexparser
from bibtexparser import *

bib_library = bibtexparser.Library()

fields = []

fields.append(bibtexparser.model.Field("author", "ö"))

entry = bibtexparser.model.Entry("ARTICLE", "test", fields)

bib_library.add(entry)

print(bib_library.entries_dict)

bibtexparser.write_file("my_new_file.bib", bib_library)

Bibtex:

@ARTICLE{test,
	author = {�}
}

Workaround
No; possibly generating a string first and then writing that manually will work (similarly to the workaround for #394).

Remaining Questions (Optional)
Please tick all that apply:

• I would be willing to to contribute a PR to fix this issue.
• This issue is a blocker, I'd be greatful for an early fix.