How to use dynamic title in frontmatter

@phmg701, Did some playing and it seems the following is working:

• Fresh install of Grav 1.17.24

• Updated /user/config/system.yaml:

  YAMLCopy

  languages:
  supported: [en, de]
  
  pages:
  frontmatter:
    process_twig: true     # Should the frontmatter be processed to replace Twig variables?
  

• Created Contact form in two languages + single thankyou page:

  TXTCopy

  user/pages
  ├── 01.home
  │   └── default.md
  ├── 02.typography
  │   └── default.md
  └── 03.contact
    ├── form.de.md
    ├── form.en.md
    └── thankyou
        └── formdata.md
  

  03.contact/form.en.md + 03.contact/form.de.md

  YAMLCopy

  ---
  title: Contact Form
  
  form:
    name: contact
  
    fields:
        name:
          label: Name
          type: text
  
    buttons:
        submit:
          type: submit
          value: Submit
  
    process:
        message: Thank you for getting in touch!
        display: thankyou
  ---
  

  formdata.md

  TWIGCopy

  ---
  title: "{{ 'TITLE'|t }}"
  process:
    twig: true
  ---
  
  ## {{ 'CONTENT'|t }}
  

• Added translation to user/themes/quark/languages.yaml

  YAMLCopy

  en:
  TITLE: Title-EN
  CONTENT: Content-EN
  
  de:
  TITLE: Title-DE
  CONTENT: Content-DE
  

• Browsed to localhost/en/contact, filled in the form and hit submit =>
  Page title is English version + content is English version
• Browsed to localhost/de/contact, filled in the form and hit submit =>
  Page title is German version + content is German version

Hope this is what you were looking for... If not, I've had some fun anyway.