chore: refactor _convert_to_standard_langcode (#2369)
This PR is one in a series of PRs for refactoring and fixing the
`languages` parameter so it can address incorrect input by users. #2293
This PR adds a dictionary for helping map fully spelled out languages to
tesseract language codes
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Co-authored-by: Roman Isecke <136338424+rbiseck3@users.noreply.github.com>
