i18n: Improve formatting an error message for multiple streams

The leading message glued paragraphs and a missing space in
_("Unable to resolve argument '{}':{}") was confusing for the
translators.

A continuations of the message also did not suport plural forms.

Both issues are fixed with this patch. The singular form will never be
used, but the many plural ones will do.

Fixes: #1480

libdnf5/base/log_event.cpp

@@ -234,19 +234,22 @@ std::string LogEvent::to_string(
                 const auto pos = module_stream.find(":");
                 module_dict[module_stream.substr(0, pos)].insert(module_stream.substr(pos + 1));
             }
-            // Create the error message describing all the streams of modules that were matched.
-            std::string error_message;
+            // Format a leading line of the error message.
+            ret.append(utils::sformat(_("Unable to resolve argument '{}':"), *spec));
+            // Describe all the streams of modules that were matched.
             for (const auto & module_dict_iter : module_dict) {
-                error_message.append(utils::sformat(
-                    _("\n  - Argument '{}' matches {} streams ('{}') of module '{}', but none of the streams are "
-                      "enabled or "
-                      "default."),
+                ret.append(utils::sformat(
+                    P_("\n  - Argument '{}' matches {} stream ('{}') of module '{}', "
+                       "but the stream is not enabled or default.",
+                       "\n  - Argument '{}' matches {} streams ('{}') of module '{}', "
+                       "but none of the streams are enabled or default.",
+                       module_dict_iter.second.size()),
                     *spec,
                     module_dict_iter.second.size(),
-                    utils::string::join(module_dict_iter.second, "', '"),
+                    utils::string::join(module_dict_iter.second, _("', '")),
                     module_dict_iter.first));
             }
-            return ret.append(utils::sformat(_("Unable to resolve argument '{}':{}"), *spec, error_message));
+            return ret;
         }
         case GoalProblem::MODULE_SOLVER_ERROR: {
             if (!solver_problems) {