Improve i18n translator documentation

docs/en_us/developers/source/i18n_translators_guide.rst

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docs/en_us/developers/source/images/join-language-team.png

docs/en_us/developers/source/images/project-maintainers.png

docs/en_us/developers/source/images/project-resources.png

docs/en_us/developers/source/images/request-new-language.png

docs/en_us/developers/source/images/send-message-button.png

docs/en_us/developers/source/images/view-team-members.png