Prevent creation of Canvas pages in a non-default language in the UI/via the entity form
**Overview** - Currently, when creating a new Canvas page, the language selector displays all languages configured on the website, including both the default language and translated languages. - This behaviour allows users to create Canvas pages directly in non-default languages. However, Canvas pages should only be created in the site's default language (source language). - For non-default languages, users should not create separate Canvas pages. Instead, translated content should be managed through the translation interface, where translations are entered against the source-language Canvas page. **Proposed Solution** - To align with the intended translation model, users should be prevented from creating Canvas pages in any language other than the site's default language. - Remove dropdown from above the title field in the sidebar
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