config.textfile_encoding (default set to 'utf-8') is rarely used. Most textfile encodings is hard-coded with 'utf-8'.

With Python 3.15 and PEP 686, explicit global encoding configuration is increasingly unnecessary because UTF-8 becomes de facto standard text encoding. Therefore I propose to:

• Deprecate config.textfile_encoding
• Replace remaining usages with explicit 'utf-8'
• Update documentation if needed