[UX] Missing translation function calls

[VasasA]

Description of the bug
node.module and standard.install are missing translation function calls needed for localization. Unable to translate some strings of the "Add content" page (Create Post) and the welcome page.

I created two PR:
backdrop/backdrop#2858
backdrop/backdrop#2866

(Don't watch the invalid closed PRs: 2859, 2860, 2864)

Testing:

1. Download the Backdrop 1.16.2
2. Replace the core/profiles/standard/standard.install file with this (2858):
   https://raw.githubusercontent.com/VasasA/backdrop/patch-1/core/profiles/standard/standard.install
3. Replace the core/modules/node/node.module file with this (2866):
   https://raw.githubusercontent.com/VasasA/backdrop/patch-10/core/modules/node/node.module
4. From https://localize.backdropcms.org/translate/languages download a translation file. Check and edit the file: It must contain the following strings: About, Title, Body, Tags, Image, Filtered HTML, Full HTML
5. Place the translation file into the following directory: ./files/translations
6. Install Backdrop CMS with the selected language.
7. Check the translated strings at the welcome page and the "Content > Add content > Post" page according to the screenshots above.

FTR, these were the respective original issues in d.org:

https://www.drupal.org/project/drupal/issues/1016006
https://www.drupal.org/project/drupal/issues/1130732

They have been closed as duplicates of either of the following:

D8: https://www.drupal.org/project/drupal/issues/2571337
D9: https://www.drupal.org/project/drupal/issues/1157426 (which the way I understand it, is basically the respective #704)

[VasasA]

Sorry, the second (2859) PR is bad. 😢

[klonos]

...also FTR, in case that PR is closed in the future, we should not be translating variables directly by wrapping them in t():

...there's more to it: https://api.backdropcms.org/api/backdrop/core%21includes%21bootstrap.inc/function/t/1