Installing a new language damages spellchecking and hyphenation (InDesign 19.4)

[perefarrando]

I have checked it again: creating a new language deactivates Spellcheck and Hyphenation features.

I posted this a while ago (https://community.adobe.com/t5/indesign-discussions/spellchecking-not-working-after-creating-a-new-l...) and I was told that someone was aware of the problem. Unfortunately, it's still not working. 

We could have a lot more languages in InDesign. For instance, in Spain we could add Basque, Galician and different variants of Spanish (for Argentina, Peru, etc.), given that their Hunspell packages are available. As of now, that is not possible. We are stuck with the list of languages installed by default.

[Mike Witherell]

I followed the rather complex directions ...

https://helpx.adobe.com/indesign/kb/add_cs_dictionaries.html

... to install a custom language. Update. I restarted ID a second, maybe third time. I ran the spell-checker on Basque tagged text and all the red squiggles went away. Now it seems to be working, ... but I'm confused at the inconsistency of that. Before it persisted in putting red squiggles under properly-tagged Basque words. Now it seems to be happy, after I did a Cmd/Ctrl+I spell check. 

[perefarrando]

The question is: Have the "red squiggles" disappeared altogether? For instance, in English, when you type ‘prblm’ instead of 'problem', is spell-checking working? In my case, the red squiggles go away for all languages.