Normalization of ä, ö,ü and ß in filters and search of duplicates

app/static/js/table-tools.js

@@ -1,4 +1,32 @@
 (() => {
+  function normalizeSearchText(value, options = {}) {
+    const caseSensitive = Boolean(options.caseSensitive);
+    const collapseWhitespace = Boolean(options.collapseWhitespace);
+    let text = String(value ?? '');
+
+    // Preserve the common German transliterations before Unicode accent
+    // folding so searches treat umlauts and their ASCII spellings equally.
+    text = text
+      .replace(/Ä/g, 'Ae')
+      .replace(/Ö/g, 'Oe')
+      .replace(/Ü/g, 'Ue')
+      .replace(/ä/g, 'ae')
+      .replace(/ö/g, 'oe')
+      .replace(/ü/g, 'ue')
+      .replace(/ẞ/g, 'SS')
+      .replace(/ß/g, 'ss')
+      .normalize('NFKD')
+      .replace(/[\u0300-\u036f]/g, '');
+
+    if (collapseWhitespace) text = text.trim().replace(/\s+/g, ' ');
+    if (!caseSensitive) text = text.toLocaleLowerCase();
+    return text;
+  }
+
+  // Standalone filters and duplicate detection use the exact same comparison
+  // rules as the generic table filters.
+  window.AssetManagerNormalizeSearchText = normalizeSearchText;
+
   const collator = new Intl.Collator(document.documentElement.lang || 'de', {
     numeric: true,
     sensitivity: 'base'
@@ -322,7 +350,7 @@
       const active = filterDefinitions
         .map(definition => ({
           definition,
-          term: definition.input?.value.trim().toLocaleLowerCase() || ''
+          term: normalizeSearchText(definition.input?.value.trim() || '')
         }))
         .filter(item => item.term);
 
@@ -350,7 +378,7 @@
           if (definition.numericFilter) {
             return !numericFilterMatches(value, term);
           }
-          return !value.toLocaleLowerCase().includes(term);
+          return !normalizeSearchText(value).includes(term);
         });
 
         row.hidden = hidden;