@nickpagz recently worked with a user that reported broken page layouts.
After review, we identified that the cause was due to the user's WPCOM account language settings. When set to Espa帽ol, certain page layouts break. They break in the preview and carry over when you choose to use the selected page layout.
Specifically, this occurred when the Maywood theme was active and the user tried to select the Maywood, Shawburn, Twenty Twenty, or Balasana home page layouts on a Simple site.
We have yet to test with other languages, themes, or page layouts. I could not reproduce on Atomic.
For page layouts to work across user language settings.
Broken page layouts.
Various -- tested across MacOS, Windows, Chrome, and Firefox.
Example of broken page layout:

Various console errors:

Slack discussion: p1593182066424300-slack-wpcom-support
22195250-hc
#user-report
Appears related to https://github.com/Automattic/jetpack/issues/15776 cc @sirreal
This is happening because the translations for the homepages in those four themes are missing for some reason, and it falls back to the default. I opened this issue when I audited the homepage templates: https://github.com/Automattic/wp-calypso/issues/42368.
This is one of the todo items there:
Locate the translations (or make them if it's never translated) for Balasana, Maywood, Shawburn, Twenty Twenty homepages. Test, fix, and deploy the translations so that we stop the confusing experience with the fallback.
I opened this issue when I audited the homepage templates: #42368.
Excellent! I totally missed that issue already being open.
Most helpful comment
This is happening because the translations for the homepages in those four themes are missing for some reason, and it falls back to the default. I opened this issue when I audited the homepage templates: https://github.com/Automattic/wp-calypso/issues/42368.
This is one of the todo items there: