Ensure translated manual pages are installed under Meson.

help/meson.build

@@ -13,6 +13,20 @@ geary_help_pages = [
   'write.page',
 ]
 
+# Meson 0.44 added support for automatically reading LINGUAS, until we
+# can depend on that, read it in outselves. Note this means if you
+# change LINGUAS, you will need remove your build directory and re-run
+# meson for it to be picked up.
+linguas = run_command(['cat', 'LINGUAS']).stdout().strip()
+langs = []
+foreach line : linguas.split('\n')
+  line = line.strip()
+  if not line.startswith('#')
+    langs += line
+  endif
+endforeach
+
 gnome.yelp(meson.project_name(),
+  languages: langs,
   sources: geary_help_pages,
 )