Use locale from config if specified, otherwise use user's environment locale

[micahellison]

Fixes #1353 by checking the config file for a locale setting. If there's no locale setting, then it uses the environment's locale instead.

🚨 Affects both the presentation and storage of dates! 🚨

I'm also going to keep this as a draft until I:

• add documentation about this feature
  • include some "gotchas" around Windows vs other environments - from my testing, it seems like Windows only uses the Control Panel's language setting, instead of any environment variables
• address concerns around automatically fetching the locale and possibly messing with the dates on existing journals (maybe only an issue for people that use %c in their timeformat?) - I don't want every entry between the 1st and 12th day of the month to suddenly get its date mangled because someone is switching their environment between en_US and en_GB, for instance
• add additional tests?
• possibly force locale in test code with mocks so that "make test" works right out of the box regardless of the developer's locale
• gracefully deal with unsupported locales instead of spewing a stack trace

If anyone else would like to work any of the above, feel free to contribute. I'll mainly be working on this on Saturdays, Pacific time.

Checklist

• I have read the contributing doc.
• I have included a link to the relevant issue number.
• I have checked to ensure there aren't other open pull requests
  for the same issue.
• I have written new tests for these changes, as needed.

[micahellison]

Finally got a basic test working on Windows and Mac after learning--to my horror!--that strftime('%c') has different behavior across OSes even if the locale is the same. Even more specific format specifiers can vary, like %A (the day of the week) which has varying capitalizations in French.

However, Ubuntu is still failing because it doesn't seem to have any of these languages. I think I either need to a) find a locale on our Ubuntu CI setup that isn't en_US, or b) install those locales before running tests. Maybe I'll tackle that next weekend.

[micahellison]

I'm closing this since I haven't made any progress on this for six months and I don't think I'm going to return to this. However, if you're working on this issue and have any questions, please feel free to @ me.