Use BCP 47 formatted string for locale

[beastbytes]

Q	A
Is bugfix?	✔️
New feature?	❌
Breaks BC?	✔️/❌

[what-the-diff[bot]]

• Changed the default locale from en_US to en-US
• Updated SimpleMessageFormatter::format() method's $locale parameter type hint and default value
• Updated Translator constructor's $locale property declaration, type hint and default value
• Added a test for the new behavior of getLocale() in TranslatorTest class

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@3aead8d). Click here to learn what that means. Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

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[darkdef]

Sorry, but I don't agree. We use primarily the POSIX system, On POSIX platforms such as Unix, Linux and others, locale identifiers are defined by ISO/IEC 15897, which is similar to the BCP 47

[darkdef]

Read this https://en.wikipedia.org/wiki/Locale_(computer_software). Section about POSIX

[samdark]

@beastbytes First of all, tyanks for contributing. What's the idea behind the pull request? Would you please elaborate a bit?

[samdark]

Fixed in https://github.com/yiisoft/translator/pull/110. Thanks for reporting it.

[darkdef]

@beastbytes I'm so sorry. I don't understood you. We fixed that bug.