For information about Web Extension i18n json, see
Concept and Usage
JSON Schema
Actually Web Extension i18n json can be imported or exported under the name of "JSON (SimpleLocalize)", but it causes confusion.
Also it would be better to optimize archive entry paths for Web Extension i18n when exporting selected translations.
In conclusion, I request support of optimizing whole workflow for each specific scenario or use case, but also leaves a general use option.