Extend language switcher support to Content Templates
> [!note] Migrated issue
>
> <!--Drupal.org comment-->
>
> <!--Migrated from issue #3590577.-->
>
> Reported by: [kunal.sachdev](https://www.drupal.org/user/3685163)
Related to !1162
### Overview
The language switcher is currently being implemented for Canvas Pages in <span dir=""> https://git.drupalcode.org/project/canvas/-/work_items/3585452</span>. However, it should also work correctly on Canvas Templates.
### Proposed resolution
Once the base Canvas Pages language switcher is complete, extend the feature to also support Canvas Templates. This includes:
* Ensuring the language switcher dropdown appears and functions correctly when switching language.
* Validating fallback behaviour (default language rendering) for templates that lack a translation in the selected language.
* Identifying and fixing any frontend or backend issues that are specific to templates.
* Adding Playwright test coverage for the language switcher on Canvas Templates.
> Related issue: [Issue #3585452](https://www.drupal.org/node/3585452)
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