I wonder if the missing `../po/LINGUAS` is a problem and what's the consequence. The lines about "warning: invalid non-blank line" seems to be related that Meson is using `gettext` to process the .desktop file where previously `intltool` was used. And the `_Keyword...` syntax is specific for `intltool`. It seems this might be a seperate task like migrating from `intltool` to `gettext` (https://stackoverflow.com/questions/62504873/i18n-merge-file-cant-translate-desktop-file). Anyway, we need to handle this in some way as the resulting .desktop file is missing items like "Name", "Comment" and "Keywords".
I think this is what the [i18n.merge_file()](https://mesonbuild.com/i18n-module.html#i18nmerge_file) function was designed for (note the 'type' keyword).