To publish a translated version of any page, you first have to clone the original page. See Clone a page

Find the cloned page in your group (e.g. main site) and replace all text with Welsh text (including title, banner text, teaser, etc.)

In the URL path settings change the url to the stub of the original page and add  /cy/ before it e.g. if the url of the English version of the page is /what-we-do/fostering-wales make the clone url  /cy/what-we-do/fostering-wales

Changing the URL alias in Drupal

click translations and language on right-hand side of the edit page and in the content language dropdown select Welsh

selecting Welsh content language in Drupal

Save the page.

Then go back to the original (English) version.

Click translations and language on right-hand side of edit page and in the content language dropdown select English, then under Welsh translation click add translation

in the add translation box, select the Welsh-language page you need by ticking the box on the right, then click select content

selecting welsh translation content in Drupal

The Welsh version is now linked to the English page

If it’s the wrong one, click Remove and start again.

When both English and Welsh pages are saved and published, a toggle switch appears so the user can switch between them

Barnardo's main header with Welsh content link