Epic: Localize MacVim and add translations #1102

This issue is used to serve as an epic to track the ongoing work to localize MacVim.

Messages

• Support Vim message translation (see :help multilang-messages) / :set lang (Add support for localized message transalations in MacVim #1070)
• Add MacVim-specific translations for MacVim-specific messages.
  • Welcome messages (some done in Add basic localized MacVim messages for some languages #1071)
  • Modified "file changes" messages
  • Etc
• Messages used by MacVim overall app itself (using NSLocalizedString). E.g. when you are quitting using Cmd-Q but have modified files.

Menus

• Support Vim menu translations (see :help multilang-menus) / :set langmenu (Macvim add localized menus #1099)
• Add Apple official translations for common menu names like "Copy" or "Font" that MacVim uses (Macvim add localized menus #1099)
• Translate remaining menu items.

User Interface (e.g. preference pane)

• Need translations.

Documentation (:help macvim / gui_mac.txt)

• Need translations