[iagno] Translate strings from about dialog.

[Arnaud B. <arnaudb src gnome org>]

commit 6c8fdb275655059dff3bb7c139253088409bb570
Author: Arnaud Bonatti <arnaud bonatti gmail com>
Date:   Sun Aug 4 16:44:25 2019 +0200

    Translate strings from about dialog.

 src/iagno.vala | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)
---
diff --git a/src/iagno.vala b/src/iagno.vala
index 3d673ea..046e6d9 100644
--- a/src/iagno.vala
+++ b/src/iagno.vala
@@ -720,13 +720,17 @@ private class Iagno : Gtk.Application, BaseApplication
             _("Arnaud Bonatti (themes)")
         };
 
-        authors = { "Ian Peters", "Robert Ancell", "Arnaud Bonatti" };
+        /* Translators: text crediting an author, in the about dialog */
+        authors = { _("Ian Peters"), _("Robert Ancell"), _("Arnaud Bonatti") };
 
-        /* Translators: about dialog text */
-        copyright = "Copyright © 1998–2008 Ian Peters\n" +
-                    "Copyright © 2013–2015 Michael Catanzaro\n" +
-                    "Copyright © 2014–2019 Arnaud Bonatti";  // TODO translation; autogen, to not change 
each year?
-        documenters = { "Tiffany Antopolski" };
+
+        /* Translators: text crediting a maintainer, in the about dialog text; the %u are replaced with the 
years of start and end */
+        copyright = _("Copyright \xc2\xa9 %u-%u – Ian Peters").printf (1998, 2008) + "\n" +
+                    _("Copyright \xc2\xa9 %u-%u – Michael Catanzaro").printf (2013, 2015) + "\n" +
+                    _("Copyright \xc2\xa9 %u-%u – Arnaud Bonatti").printf (2014, 2019);
+
+        /* Translators: text crediting a documenter, in the about dialog */
+        documenters = { _("Tiffany Antopolski") };
         logo_icon_name = "org.gnome.Reversi";
         program_name = PROGRAM_NAME;