utils.l10n: use DEFAULT_LANGUAGE_CODE if locale lookup fails (#3055)
utils.l10n: use DEFAULT_LANGUAGE_CODE if locale lookup fails (#3055)

instead of using DEFAULT_LANGUAGE.

This will prevent the LookupError from being raised unnecessarily
by the Localization._parse_locale_code call afterwards.
melmorabity/streamlink,chhe/streamlink,beardypig/streamlink,gravyboat/streamlink,streamlink/streamlink,melmorabity/streamlink,beardypig/streamlink,bastimeyer/streamlink,streamlink/streamlink,chhe/streamlink,gravyboat/streamlink,bastimeyer/streamlink