A lot of the content in translatewiki and Incubator is in both Latin and Cyrillic script.
Most of the publishing and the education in this language is in the Republic of Azerbaijan, and it's done in the Latin script. This is also the script on which the small community in the Incubator asked to standardize. Nevertheless, the Cyrillic script is used by the Talysh community in Russia, which is small, but quite active online. The Arabic script is used in Iran, but only rarely, so it's not proposed here.
The converter will probably be the simplest in MediaWiki to date, because the correspondence between the letters is perfectly one to one, without digraphs, diacritics, or special rules.
[v] Add a converter ([[ https://gerrit.wikimedia.org/r/c/mediawiki/core/+/616511 | patch ]])
[ ] Split the Messages file. At the moment, the magic words are in Cyrillic and the namespaces are in Latin. The standard should be in Latin, and the Cyrillic names can perhaps be kept as aliases, if at all needed. ([[ https://gerrit.wikimedia.org/r/c/mediawiki/core/+/662042 | patch ]])
[v] Update language-data in GitHub. ([[ https://github.com/wikimedia/language-data/pull/142 | patch ]])
[v] Configure translatewiki ([[ https://gerrit.wikimedia.org/r/c/translatewiki/+/666351/2/groups/MediaWiki/MediaWiki.yaml | patch 1 ]], [[ https://gerrit.wikimedia.org/r/c/translatewiki/+/617088 | patch 2 ]]).