I run WordPress 5.1 in all my sites.
I upload my own translations because I don’t like some aspects of the “official” ones. GlotPress is a very good way of making collaborative translations, but at the same time we should admit that the quality of many of them is, to put it politely, quite questionable.
Anyway, I do not want to criticize the efforts of the community, which I respect and admire. I only want to understand the mechanisms of the new translation system, as described here, https://make.www.ads-software.com/core/2018/11/09/new-javascript-i18n-support-in-wordpress/, and use it for my own particular needs.
As for Jetpack, apart from the “official” .po and .mo files, which are downloaded automatically to /wp-content/languages/folder when user clicks the Update button, there is a /wp-content/plugins/jetpack/languages/json/ folder, which contains the translation .json files necessary for translating Jetpack admin pages. In other words: .po and .mo files are a necessary, but not a sufficient condition for translating Jetpack.
My question is very simple: if Jetpack is fully translated to Spanish in GlotPress (and it is), why Jetpack blocks are not translated, even after updating all translation files? And this is only a part of the problem: as I have said before, many plugins which add blocks to Gutenberg editor lack appropriate translations for them. In some cases, these translations only translate admin pages, but not the name and the options of the blocks.
In my humble opinion, the correct and thorough translation of non native Gutenberg blocks is a crucial point in the development and success of the new edition interface established by WordPress 5.0. I like Gutenberg very much and I don’t have any personal problem with texts in English, but at the same time I consider the current lack of translations for many, many blocks, a very serious problem for those users who feel uncomfortable with English words.
In addition to about 12 personal sites (most of them are test sites), I manage more than 190 sites for schools in Navarre, Spain, and I feel very worried about the current situation. Until version 5.0, I was able to modify standard translations when I needed it, by means of custom .po and .mo files; now I do not know how to get proper and thorough translations.