* Add Guideline for i18n engine
* Update Guideline according to changes in i18n engine.
* Update examples in Guideline
* typo
* improve i18n guideline: add table for better view, use single quotes for js strings, fix description for testing, use uniq "message id" name
* fix readme description for guideline
Co-authored-by: maryia-lapata "mary.lopato@gmail.com"