diff --git a/astro.config.mjs b/astro.config.mjs
index 54a4fd4..b98f686 100644
--- a/astro.config.mjs
+++ b/astro.config.mjs
@@ -5,7 +5,7 @@ import tailwindcss from '@tailwindcss/vite';
 export default defineConfig({
   output: 'static',
   site: process.env.PUBLIC_SITE_URL ?? 'https://dev.blackbrowedlabs.com',
-  trailingSlash: 'never',
+  trailingSlash: 'always',
   i18n: {
     defaultLocale: 'de',
     locales: ['de', 'en'],
diff --git a/src/components/SiteFooter.astro b/src/components/SiteFooter.astro
index 9e5b6ab..b4b26cf 100644
--- a/src/components/SiteFooter.astro
+++ b/src/components/SiteFooter.astro
@@ -14,11 +14,11 @@ const path = Astro.url.pathname;
 const locale = getLocaleFromPath(path);
 const t = getUiStrings(locale).footer;
 
-const productsHref = locale === 'de' ? '/produkte' : '/en/products';
-const aboutHref = locale === 'de' ? '/ueber' : '/en/about';
-const contactHref = locale === 'de' ? '/kontakt' : '/en/contact';
-const legalHref = locale === 'de' ? '/impressum' : '/en/legal';
-const privacyHref = locale === 'de' ? '/datenschutz' : '/en/privacy';
+const productsHref = locale === 'de' ? '/produkte/' : '/en/products/';
+const aboutHref = locale === 'de' ? '/ueber/' : '/en/about/';
+const contactHref = locale === 'de' ? '/kontakt/' : '/en/contact/';
+const legalHref = locale === 'de' ? '/impressum/' : '/en/legal/';
+const privacyHref = locale === 'de' ? '/datenschutz/' : '/en/privacy/';
 ---
 
 <footer class="site-footer">
diff --git a/src/components/SiteHeader.astro b/src/components/SiteHeader.astro
index 0beee37..ca85947 100644
--- a/src/components/SiteHeader.astro
+++ b/src/components/SiteHeader.astro
@@ -18,13 +18,13 @@ const path = Astro.url.pathname;
 const locale = getLocaleFromPath(path);
 const t = getUiStrings(locale);
 
-const homeHref = locale === 'de' ? '/' : '/en';
-const productsHref = locale === 'de' ? '/produkte' : '/en/products';
-const productsActive = path === productsHref || path.startsWith(productsHref + '/');
-const aboutHref = locale === 'de' ? '/ueber' : '/en/about';
-const aboutActive = path === aboutHref || path === aboutHref + '/';
-const contactHref = locale === 'de' ? '/kontakt' : '/en/contact';
-const contactActive = path === contactHref || path === contactHref + '/';
+const homeHref = locale === 'de' ? '/' : '/en/';
+const productsHref = locale === 'de' ? '/produkte/' : '/en/products/';
+const productsActive = path.startsWith(productsHref);
+const aboutHref = locale === 'de' ? '/ueber/' : '/en/about/';
+const aboutActive = path === aboutHref;
+const contactHref = locale === 'de' ? '/kontakt/' : '/en/contact/';
+const contactActive = path === contactHref;
 ---
 
 <header class="site-header">
diff --git a/src/content/editorial/contact.de.md b/src/content/editorial/contact.de.md
index b7e90c5..f4e5a8b 100644
--- a/src/content/editorial/contact.de.md
+++ b/src/content/editorial/contact.de.md
@@ -10,4 +10,4 @@ Code und Produktentwicklung auf GitHub: [blackbrowed-labs](https://github.com/bl
 
 ## Hinweis zum Datenschutz
 
-Die Felder Name, E-Mail-Adresse und Nachricht werden ausschließlich zur Bearbeitung Ihrer Anfrage verarbeitet und an das E-Mail-Postfach lars@blackbrowedlabs.com (IONOS) zugestellt. Rechtsgrundlage ist Art. 6 Abs. 1 lit. b DSGVO bei vorvertraglichen Anfragen bzw. Art. 6 Abs. 1 lit. f DSGVO bei sonstigen Anfragen. Die Speicherung und Aufbewahrung erfolgt gemäß Abschnitt 5 der [Datenschutzerklärung](/datenschutz).
+Die Felder Name, E-Mail-Adresse und Nachricht werden ausschließlich zur Bearbeitung Ihrer Anfrage verarbeitet und an das E-Mail-Postfach lars@blackbrowedlabs.com (IONOS) zugestellt. Rechtsgrundlage ist Art. 6 Abs. 1 lit. b DSGVO bei vorvertraglichen Anfragen bzw. Art. 6 Abs. 1 lit. f DSGVO bei sonstigen Anfragen. Die Speicherung und Aufbewahrung erfolgt gemäß Abschnitt 5 der [Datenschutzerklärung](/datenschutz/).
diff --git a/src/content/editorial/contact.en.md b/src/content/editorial/contact.en.md
index 2801236..8abc7b0 100644
--- a/src/content/editorial/contact.en.md
+++ b/src/content/editorial/contact.en.md
@@ -10,4 +10,4 @@ Code and product development on GitHub: [blackbrowed-labs](https://github.com/bl
 
 ## Privacy notice
 
-The fields Name, Email address, and Message are processed solely to handle your inquiry and are delivered to the email mailbox lars@blackbrowedlabs.com (IONOS). The legal basis is Art. 6 (1) (b) GDPR for pre-contractual inquiries or Art. 6 (1) (f) GDPR for other inquiries. Storage and retention follow Section 5 of the [Privacy Policy](/en/privacy).
+The fields Name, Email address, and Message are processed solely to handle your inquiry and are delivered to the email mailbox lars@blackbrowedlabs.com (IONOS). The legal basis is Art. 6 (1) (b) GDPR for pre-contractual inquiries or Art. 6 (1) (f) GDPR for other inquiries. Storage and retention follow Section 5 of the [Privacy Policy](/en/privacy/).
diff --git a/src/lib/i18n.ts b/src/lib/i18n.ts
index 75421c2..8ae211b 100644
--- a/src/lib/i18n.ts
+++ b/src/lib/i18n.ts
@@ -9,12 +9,16 @@
 import type { Locale } from '../i18n';
 
 /**
- * Canonical path form: leading slash, no trailing slash, except the
- * root path which is just "/".
+ * Canonical path form: leading slash, trailing slash kept (or added),
+ * except the root path which is just "/".
+ * Phase E (trailing-slash alignment) inverted this from the original
+ * "strip trailing slash" behaviour — kept symmetric with Astro's
+ * `trailingSlash: 'always'` so counterpart-map lookups and slug splits
+ * use the same shape Astro emits.
  */
 function canonicalise(path: string): string {
   if (path === '' || path === '/') return '/';
-  return path.endsWith('/') ? path.slice(0, -1) : path;
+  return path.endsWith('/') ? path : `${path}/`;
 }
 
 /**
@@ -23,25 +27,25 @@ function canonicalise(path: string): string {
  * switcher renders the missing side as aria-disabled.
  */
 const counterparts: Record<string, string> = {
-  '/': '/en',
-  '/en': '/',
-  '/ueber': '/en/about',
-  '/en/about': '/ueber',
-  '/kontakt': '/en/contact',
-  '/en/contact': '/kontakt',
-  '/impressum': '/en/legal',
-  '/en/legal': '/impressum',
-  '/datenschutz': '/en/privacy',
-  '/en/privacy': '/datenschutz',
-  '/produkte': '/en/products',
-  '/en/products': '/produkte',
-  '/404': '/en/404',
-  '/en/404': '/404',
+  '/': '/en/',
+  '/en/': '/',
+  '/ueber/': '/en/about/',
+  '/en/about/': '/ueber/',
+  '/kontakt/': '/en/contact/',
+  '/en/contact/': '/kontakt/',
+  '/impressum/': '/en/legal/',
+  '/en/legal/': '/impressum/',
+  '/datenschutz/': '/en/privacy/',
+  '/en/privacy/': '/datenschutz/',
+  '/produkte/': '/en/products/',
+  '/en/products/': '/produkte/',
+  '/404/': '/en/404/',
+  '/en/404/': '/404/',
 };
 
 export function getLocaleFromPath(path: string): Locale {
   const canonical = canonicalise(path);
-  return canonical === '/en' || canonical.startsWith('/en/') ? 'en' : 'de';
+  return canonical.startsWith('/en/') ? 'en' : 'de';
 }
 
 export function getCounterpartUrl(path: string): string | null {
diff --git a/src/pages/en/about.astro b/src/pages/en/about.astro
index b8331e3..88b53f7 100644
--- a/src/pages/en/about.astro
+++ b/src/pages/en/about.astro
@@ -29,7 +29,7 @@ const t = getUiStrings('en');
 <BaseLayout title={`${title} — Blackbrowed Labs`} description={description}>
   <nav class="breadcrumb" aria-label={t.breadcrumb.ariaLabel}>
     <div class="breadcrumb__inner">
-      <a href="/en">Blackbrowed Labs</a>
+      <a href="/en/">Blackbrowed Labs</a>
       <span class="breadcrumb__sep" aria-hidden="true">/</span>
       <span class="breadcrumb__current" aria-current="page">{title}</span>
     </div>
diff --git a/src/pages/en/contact.astro b/src/pages/en/contact.astro
index f63a88e..a0b403b 100644
--- a/src/pages/en/contact.astro
+++ b/src/pages/en/contact.astro
@@ -23,7 +23,7 @@ const t = getUiStrings('en');
 <BaseLayout title={`${title} — Blackbrowed Labs`} description={description}>
   <nav class="breadcrumb" aria-label={t.breadcrumb.ariaLabel}>
     <div class="breadcrumb__inner">
-      <a href="/en">Blackbrowed Labs</a>
+      <a href="/en/">Blackbrowed Labs</a>
       <span class="breadcrumb__sep" aria-hidden="true">/</span>
       <span class="breadcrumb__current" aria-current="page">{title}</span>
     </div>
diff --git a/src/pages/en/legal.astro b/src/pages/en/legal.astro
index 68f33bf..068f8e2 100644
--- a/src/pages/en/legal.astro
+++ b/src/pages/en/legal.astro
@@ -20,7 +20,7 @@ const description =
 <BaseLayout title={`${title} — Blackbrowed Labs`} description={description}>
   <nav class="breadcrumb" aria-label={t.breadcrumb.ariaLabel}>
     <div class="breadcrumb__inner">
-      <a href="/en">Blackbrowed Labs</a>
+      <a href="/en/">Blackbrowed Labs</a>
       <span class="breadcrumb__sep" aria-hidden="true">/</span>
       <span class="breadcrumb__current" aria-current="page">{title}</span>
     </div>
diff --git a/src/pages/en/privacy.astro b/src/pages/en/privacy.astro
index 3d7f9aa..cbd3e0d 100644
--- a/src/pages/en/privacy.astro
+++ b/src/pages/en/privacy.astro
@@ -58,7 +58,7 @@ const tocItems = [
 
   <nav class="breadcrumb" aria-label={t.breadcrumb.ariaLabel}>
     <div class="breadcrumb__inner">
-      <a href="/en">Blackbrowed Labs</a>
+      <a href="/en/">Blackbrowed Labs</a>
       <span class="breadcrumb__sep" aria-hidden="true">/</span>
       <span class="breadcrumb__current" aria-current="page">{title}</span>
     </div>
diff --git a/src/pages/en/products/[slug].astro b/src/pages/en/products/[slug].astro
index 295869d..1e7cb53 100644
--- a/src/pages/en/products/[slug].astro
+++ b/src/pages/en/products/[slug].astro
@@ -74,9 +74,9 @@ const renderedReleaseBodies: string[] = await Promise.all(
 <BaseLayout title={`${title} — Blackbrowed Labs`} description={description}>
   <nav class="breadcrumb" aria-label={t.breadcrumb.ariaLabel}>
     <div class="breadcrumb__inner">
-      <a href="/en">Blackbrowed Labs</a>
+      <a href="/en/">Blackbrowed Labs</a>
       <span class="breadcrumb__sep" aria-hidden="true">/</span>
-      <a href="/en/products">Products</a>
+      <a href="/en/products/">Products</a>
       <span class="breadcrumb__sep" aria-hidden="true">/</span>
       <span class="breadcrumb__current" aria-current="page">{entry.data.name}</span>
     </div>
diff --git a/src/pages/en/products/index.astro b/src/pages/en/products/index.astro
index a063302..a1e8948 100644
--- a/src/pages/en/products/index.astro
+++ b/src/pages/en/products/index.astro
@@ -20,7 +20,7 @@ const description =
 <BaseLayout title={`${title} — Blackbrowed Labs`} description={description}>
   <nav class="breadcrumb" aria-label={t.breadcrumb.ariaLabel}>
     <div class="breadcrumb__inner">
-      <a href="/en">Blackbrowed Labs</a>
+      <a href="/en/">Blackbrowed Labs</a>
       <span class="breadcrumb__sep" aria-hidden="true">/</span>
       <span class="breadcrumb__current" aria-current="page">{t.productsIndex.breadcrumb}</span>
     </div>
@@ -52,11 +52,11 @@ const description =
             {products.map((entry) => (
               <li class="products-index__item">
                 <h2 class="products-index__name">
-                  <a href={`/en/products/${entry.data.slug}`}>{entry.data.name}</a>
+                  <a href={`/en/products/${entry.data.slug}/`}>{entry.data.name}</a>
                 </h2>
                 <p class="products-index__tagline">{entry.data.tagline}</p>
                 <p class="products-index__description">{entry.data.description}</p>
-                <a class="products-index__more" href={`/en/products/${entry.data.slug}`}>
+                <a class="products-index__more" href={`/en/products/${entry.data.slug}/`}>
                   {t.productsIndex.populatedArrowLabel}
                 </a>
               </li>
diff --git a/src/pages/produkte/[slug].astro b/src/pages/produkte/[slug].astro
index ff0671a..f315291 100644
--- a/src/pages/produkte/[slug].astro
+++ b/src/pages/produkte/[slug].astro
@@ -108,7 +108,7 @@ const renderedReleaseBodies: string[] = await Promise.all(
     <div class="breadcrumb__inner">
       <a href="/">Blackbrowed Labs</a>
       <span class="breadcrumb__sep" aria-hidden="true">/</span>
-      <a href="/produkte">Produkte</a>
+      <a href="/produkte/">Produkte</a>
       <span class="breadcrumb__sep" aria-hidden="true">/</span>
       <span class="breadcrumb__current" aria-current="page">{entry.data.name}</span>
     </div>
diff --git a/src/pages/produkte/index.astro b/src/pages/produkte/index.astro
index b0b77e2..19916ce 100644
--- a/src/pages/produkte/index.astro
+++ b/src/pages/produkte/index.astro
@@ -62,11 +62,11 @@ const description =
             {products.map((entry) => (
               <li class="products-index__item">
                 <h2 class="products-index__name">
-                  <a href={`/produkte/${entry.data.slug}`}>{entry.data.name}</a>
+                  <a href={`/produkte/${entry.data.slug}/`}>{entry.data.name}</a>
                 </h2>
                 <p class="products-index__tagline">{entry.data.tagline}</p>
                 <p class="products-index__description">{entry.data.description}</p>
-                <a class="products-index__more" href={`/produkte/${entry.data.slug}`}>
+                <a class="products-index__more" href={`/produkte/${entry.data.slug}/`}>
                   {t.productsIndex.populatedArrowLabel}
                 </a>
               </li>