core VS ESP-Now

Some libraries support ways to handle missing translations (e.g., TranslocoMissingHandler from Transloco or MissingTranslationHandler   from ngx-translate). So that's a way to find out any missing translations, but that's quite manual because you have to go over every part of the served application.

ngx-translate

It was rather painless. We are using ngx-translate which seems dead at this point but works fine in 16 (seems to have gotten a recent commit).

The problem with Angular 15 was the Ivy engine. And it wasn't fixed, maybe you're not affected. https://github.com/ngx-translate/core/issues/1185

He talks about it more here: https://github.com/ngx-translate/core/issues/783

Ngx-translate is not updated anymore. Latest version is a year old. It's still not abandoned but it seems like the developer moved on to work on Angular i18n.

Just to refer to the original docs: https://github.com/ngx-translate/core

One of the common pitfalls when using i18n are large translation files size and inability to split them in order to hide parts of your application from prying eyes. Some solutions like Angular built-in implementation are really powerful and SEO compatible but require a lot of preparation and do not support switching languages on the fly in development mode (which was causing troubles at least in version 9); other solutions like ngx-translate require you to install several packages and still don’t support splitting up a single language.

There's some other good tutorials for it as well, https://randomnerdtutorials.com/?s=esp-now and https://github.com/HarringayMakerSpace/ESP-Now

For power, I'd recommend Li-Ion primary (non-rechargeable) cells, whatever size works best for you. Those have essentially zero internal leakage and a 5 year shelf-life. If you've done it all correctly, it's conceivable it could be 5 years before you need to change the batteries (on top of a 30' ladder). You'd need a small high-efficiency buck converter to drop the 6.8V batteries down to 3.3V for the ESP, with a separate switched 5V linear regulator (one with a SHUTDOWN pin) to power the servos when they need to be driven. The ESP will consume 16-20uA in Deep Sleep, and the buck converter should mostly be off, except for when the ESP wakes every 3.5 hours (maximum Deep Sleep interval). If you're already using ESP-NOW to talk to the vent ESPs, then you could do a 'vent changed' check every time it wakes, otherwise it's more efficient to go back to Sleep quickly and wait until 12-24 hours has elapsed before you fire up a full WiFi connection. Not counting buck inefficiencies and servo movements, the ESP would only consume about 175mAh per year. The batteries will expire before they empty, maybe in 6-7 years.

I presume you've seen Anthony Elder's examples? He got a single ESP to act as hub by restarting it. In a low-traffic environment that'd work. There was discussion and a new PR to speed up the reconnect time using WIFI_RESUME that's been merged in the git repo, which should make a single-ESP hub faster to respond. You'd need a little fault checking in case the BSSID changes of course, but for the normal case things would be faster.