1 WUMT does not disable anything, it is just a means of listing & downloading updates.
Perhaps you used a thing called WUMT WrapperScript / SledgeHammer to disable WU and set up WUMT in its place? -
Download Sledgehammer (formerly WUMT Wrapper Script) - MajorGeeks
Personally, I avoid automatic updates by just setting my network connections to metered and almost all Windows updates are prevented [there's one small & inconsequential one,
KB4023057, that slips through once or sometimes twice a year] so I don't bother with any fancy measures such as disabling WU. Because of the metered setting, WU simply does not download or install anything.
Set Wireless Network Metered Connection - TenForumsTutorials
Set Ethernet Connection as Metered or Unmetered - TenForumsTutorials
This is my Registry key after applying these changes. All network connections are metered including the Default i.e. all future WiFi networks that I might connect to.
2 If you have used SledgeHammer to disable WU then you have indeed disabled Defender malware definition updates & platform updates. My metered settings also have this effect.
Setting them up yourself to run automatically [outside of WU] is fairly straightforward.
See Option 3 of
Update ... Microsoft Defender - TenForumsTutorials
Whilst that tutorial & many other articles refer to malware definition updates, updating them will also include updating the Defender platform [the utility itself].
3 Windows Store app updates run outside of WU. So do updates for MSOffice 2016 & later versions. I don't know about language packs.
4 I update my Windows by running
WUMT itself [i.e. not SledgeHammer],
WUMgr or an equivalent to list available updates then I search
TenForums News for threads with their KB numbers in the titles. There's a News article for practically every update & almost all of them have a direct download link for the update.
All the best,
Denis