Add support for i18n in the cli

[hdiniz]

Please check if the PR fulfills these requirements

• The PR has no duplicates (please search among the Pull Requests before creating one)
• The PR follows our contributing guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce?
  Using the function i18n.Tr("message", ...) its now possible to have localised messages in the cli.
  Localisation files are generated for each supported language.

• What is the current behavior?
  No i18n support

• What is the new behavior?
  To localise messages, use the function i18n.Tr. The message will be localised with the locale set via i18n.SetLocale(..)

• Does this PR introduce a breaking change?
  No

• Other information:

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See how to contribute

[cmaglie]

I've tested:

• task i18n:update (so tr(..) and i18n.Tr(..) calls detection)
• task i18n:push and pull from transifex
• PR sanity check on CI (checks fail if the submitter didn't run i18n:update)
• various extreme conditions on missing translations
• language setting detection on Linux

I did not test:

• language settings detection on Windows and Mac
• daily translation push to transifex
• weekly translations pull from transifex into a PR

BTW I think that the above may be fixed in a later PR (if needed) after testing the whole system for a while.

[rsora]

👍