style: consistent back button and some translations

DESIGN_DUIDELINES.md

@@ -46,19 +46,35 @@ Every authenticated page should follow the same structure:
 **MUST:** Use `<.header>` on every page (except login/public pages).  
 **SHOULD:** Put short explanations into `<:subtitle>` rather than sprinkling random text blocks.
 
-**Template:**
+### 2.2 Edit/New form header: Back button left (mandatory)
+
+For LiveViews that render an edit or new form (e.g. member, group, role, user, custom field, membership fee type):
+
+- **MUST:** Provide a **Back** button on the **left** side of the header using the `<:leading>` slot (same as data fields: Back left, title next, primary action on the right).
+- **MUST:** Use the same pattern everywhere: Back button with `variant="neutral"`, arrow-left icon, and label “Back”. It navigates to the previous context (e.g. detail page or index) via a `return_path`-style helper.
+- **SHOULD:** Place the primary action (e.g. “Save”) in `<:actions>` on the right.
+- **Rationale:** Users expect a consistent way to leave the form without submitting; Back left matches the data fields edit view and keeps primary actions on the right.
+
+**Template for form pages:**
 ```heex
 <.header>
-  Title
-  <:subtitle>Short explanation of what the page is for.</:subtitle>
+  <:leading>
+    <.button navigate={return_path(@return_to, @resource)} variant="neutral">
+      <.icon name="hero-arrow-left" class="size-4" />
+      {gettext("Back")}
+    </.button>
+  </:leading>
+  Page title (e.g. “Edit Member” or “New User”)
+  <:subtitle>Short explanation.</:subtitle>
   <:actions>
-    <.button variant="primary" navigate={...}>Primary action</.button>
+    <.button phx-disable-with={gettext("Saving...")} variant="primary" type="submit">
+      {gettext("Save")}
+    </.button>
   </:actions>
 </.header>
+```
 
-<div class="mt-6 space-y-6">
-  <!-- Sections / Cards / Tables -->
-</div>
+If the `<.header>` is outside the `<.form>`, the submit button must reference the form via the `form` attribute (e.g. `form="user-form"`).
 
 ## 3) Typography (system)