add definition to first abbreviation instance

example.typ

@@ -1,7 +1,7 @@
 #import "template/template.typ": *
 
 #show: tultemplate.with(
-  "classic", "fm", "en",
+  "classic", "fm", "cs",
   title: "Návod na použití Typst TUL šablony",
   author: "Ondřej Mekina",
 )

template/abbreviations.typ

@@ -11,11 +11,19 @@
         );
       }
       abbrs.insert(abbreviation, text);
+    }  else {
+      if type(text) != type(none) {
+        panic("redefinition of abbreviation '" + abbreviation + "'");
+      }
     }
     "(" + abbrs.pairs().map((v) => { v.at(0) + ":\"" + v.at(1) + "\"" }).join(",") + ")"
   });
+  if type(text) != type(none) {
+    text + " (" + abbreviation + ")";
+  } else {
     abbreviation;
   }
+}
 
 #let abbrlist() = {
   let abbreviations = abbreviations.final();