Improve some notification and translation docs

[KoBeWi]

Closes #89804

[YeldhamDev]

Before this is merged, I would like to tackle a way that makes the current behavior people use to update texts still work.

See below.

[Kiisu-Master]

On the NOTIFICATION_TRANSLATION_CHANGED doc also mention it gets sent when setting auto translate mode. It seems like a important thing and I kind of forgot about that. When creating the issue, I thought it only gets sent when changing locale or smth (as I have never had a reason to set the auto translate mode at runtime).

[YeldhamDev]

I thought it only gets sent when changing locale or smth

The current naming definitely doesn't help. We discussed in the dev chat that also the opportunity arrives, to replace _CHANGED with _UPDATED.

Also, I'm afraid that people will have to adapt to the new way of doing it. As I can't think of a way to support the old behavior without over-complicating things.

[KoBeWi]

On the NOTIFICATION_TRANSLATION_CHANGED doc also mention it gets sent when setting auto translate mode.

Done.

[akien-mga]

Thanks!