🌐 Sync Translations + Update README Progress Table (#3807)

### Description of Changes

This Pull Request was automatically generated to synchronize updates to
translation files and documentation. Below are the details of the
changes made:

#### **1. Synchronization of Translation Files**
- Updated translation files (`messages_*.properties`) to reflect changes
in the reference file `messages_en_GB.properties`.
- Ensured consistency and synchronization across all supported language
files.
- Highlighted any missing or incomplete translations.

#### **2. Update README.md**
- Generated the translation progress table in `README.md`.
- Added a summary of the current translation status for all supported
languages.
- Included up-to-date statistics on translation coverage.

#### **Why these changes are necessary**
- Keeps translation files aligned with the latest reference updates.
- Ensures the documentation reflects the current translation progress.

---

Auto-generated by [create-pull-request][1].

[1]: https://github.com/peter-evans/create-pull-request

---------

Co-authored-by: stirlingbot[bot] <195170888+stirlingbot[bot]@users.noreply.github.com>

stirling-pdf/src/main/resources/messages_nl_NL.properties

@@ -525,6 +525,10 @@ home.addImage.title=Afbeelding toevoegen
 home.addImage.desc=Voegt een afbeelding toe op een specifieke locatie in de PDF
 addImage.tags=img,jpg,foto
 
+home.attachments.title=Add Attachments
+home.attachments.desc=Add or remove embedded files (attachments) to/from a PDF
+attachments.tags=embed,attach,file,attachment,attachments
+
 home.watermark.title=Watermerk toevoegen
 home.watermark.desc=Voeg een aangepast watermerk toe aan je PDF-document.
 watermark.tags=Tekst,herhalend,label,eigen,copyright,handelsmerk,img,jpg,foto
@@ -1205,6 +1209,12 @@ addImage.everyPage=Elke pagina?
 addImage.upload=Afbeelding toevoegen
 addImage.submit=Afbeelding toevoegen
 
+#attachments
+attachments.title=Add Attachments
+attachments.header=Add attachments
+attachments.description=Allows you to add attachments to the PDF
+attachments.descriptionPlaceholder=Enter a description for the attachments...
+attachments.addButton=Add Attachments
 
 #merge
 merge.title=Samenvoegen
@@ -1594,6 +1604,7 @@ fileChooser.dragAndDropPDF=Drag & Drop PDF file
 fileChooser.dragAndDropImage=Drag & Drop Image file
 fileChooser.hoveredDragAndDrop=Drag & Drop file(s) here
 fileChooser.extractPDF=Extracting...
+fileChooser.addAttachments=drag & drop attachments here
 
 #release notes
 releases.footer=Releases