[i18n] how to 'fully' customize translation

I’m trying to customize the translation for specific languages by changing the corresponding JSON files found in the i18n folder. It seems that only some of the front-end string translations can be customized, e.g. the string for town-square channel; while others not, e.g. the string for public channel. I wonder if it’s possible to customize all the front-end string translations? And apart from the translations files in i18n folder, are there other places (db tables, etc.) I need to look into?