Yes, strings are generated in the resx files per page. Radzen will try to generate unique keys for as many as possible component properties however in some cases you will need to manually define and use the resx entries.
But when I check my MainLayout.xx-XX.resx files, there are entries from items that aren't exist or aren't exist anymore or got renamed.
Doesn't the IDE modify it?
eg
this items aren't exist anymore or got renamed.
Only default culture resx files are overwritten on subsequent runs, other culture resx files will be merged with what's generated for default culture resx - no entries will be deleted.