LanguageAccept.best_match fails matching langs with extras to bare langs

[golyalpha]

Werkzeug version: 0.16.0

Used through Flask.

In flask:

print("Accept-Language: %s" % (request.accept_languages,))
print("Best match: %s" % (request.accept_languages.best_match(["en"]),))

Comes back with:

Accept-Language: en-gb
Best match: None

When request comes from Safari. UA:

Mozilla/5.0 (iPhone; CPU iPhone OS 13_0 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/13.0 Mobile/15E148 Safari/604.1

According to #450, Best match should be en instead.

[davidism]

It's marked for the 1.0.0 milestone.